diff --git a/apps/gridcraft-cli/src/check.rs b/apps/gridcraft-cli/src/check.rs
index bbd3103d8..318b43aad 100644
--- a/apps/gridcraft-cli/src/check.rs
+++ b/apps/gridcraft-cli/src/check.rs
@@ -1353,456 +1353,4 @@ fn print_human(reports: &[FileReport], opts: &Options) {
 }
 
 #[cfg(test)]
-mod tests {
-    #![allow(clippy::unwrap_used)]
-    use std::io::Write as _;
-    use std::sync::Arc;
-
-    use gridcraft_engine::model::Formula;
-
-    use super::*;
-
-    #[test]
-    fn discovery_reports_a_directory_read_error() {
-        let path = std::env::temp_dir().join(format!("gridcraft-check-not-a-directory-{}", std::process::id()));
-        std::fs::write(&path, "not a directory").unwrap();
-        let mut discovery = Discovery::default();
-        let mut seen = std::collections::HashSet::new();
-        assert!(walk(&path, 0, &mut discovery, &mut seen));
-        assert!(discovery.files.is_empty());
-        assert_eq!(discovery.failures.len(), 1);
-        assert_eq!(discovery.failures[0].path, path.to_string_lossy());
-        assert!(discovery.failures[0].error.as_ref().unwrap().contains("cannot read directory"));
-        let _ = std::fs::remove_file(path);
-    }
-
-    #[test]
-    fn discovery_reports_omissions_only_after_the_file_limit() {
-        let mut discovery = Discovery { files: vec![PathBuf::from("book.xlsx"); MAX_FILES - 1], ..Default::default() };
-        assert!(discovery.add_file(PathBuf::from("last.xlsx")));
-        assert!(discovery.failures.is_empty());
-        assert!(!discovery.add_file(PathBuf::from("omitted.xlsx")));
-        assert_eq!(discovery.files.len(), MAX_FILES);
-        assert_eq!(discovery.failures[0].path, "omitted.xlsx");
-        assert!(discovery.failures[0].error.as_ref().unwrap().contains("file limit"));
-    }
-
-    fn at(a1: &str) -> CellRef {
-        CellRef::parse(a1).unwrap()
-    }
-
-    /// A workbook whose cells are `(A1, input, cached value)`: an input starting with `=` is a
-    /// formula with that cached value, anything else a constant.
-    fn book(cells: &[(&str, &str, Value)]) -> Workbook {
-        let mut wb = Workbook::new();
-        let sh = wb.sheet_mut(0).unwrap();
-        for (a1, input, cached) in cells {
-            let cell = if input.starts_with('=') {
-                Cell { value: cached.clone(), formula: Some(Arc::new(Formula::new(input))), ..Default::default() }
-            } else {
-                Cell::value(cached.clone())
-            };
-            sh.set_cell(at(a1), cell);
-        }
-        wb
-    }
-
-    fn check(wb: &Workbook, opts: &Options) -> FileReport {
-        let bytes = gridcraft_engine::io::save_bytes(wb, "t.xlsx").unwrap();
-        check_bytes("t.xlsx", &bytes, opts)
-    }
-
-    fn n(x: f64) -> Value {
-        Value::number(x)
-    }
-
-    #[test]
-    fn matching_cached_values_pass() {
-        let wb = book(&[("A1", "2", n(2.0)), ("B1", "=A1*3", n(6.0)), ("C1", "=A1&\"x\"", Value::text("2x")), ("D1", "=A1>1", Value::Bool(true))]);
-        let r = check(&wb, &Options::default());
-        assert_eq!(r.error, None);
-        assert_eq!((r.calc.formula_cells, r.calc.checked, r.calc.matched, r.calc.mismatched), (3, 3, 3, 0));
-        assert!(r.is_clean(), "{r:?}");
-    }
-
-    #[test]
-    fn wrong_cached_value_is_a_mismatch_and_ranks_its_function() {
-        // Excel "said" SUM gives 7; GridCraft computes 6. C1 reads B1 and is consistent with
-        // Excel's 7, so it mismatches too, but only as a downstream effect.
-        let wb = book(&[("A1", "2", n(2.0)), ("A2", "4", n(4.0)), ("B1", "=SUM(A1:A2)", n(7.0)), ("C1", "=B1+1", n(8.0))]);
-        let r = check(&wb, &Options::default());
-        assert_eq!((r.calc.checked, r.calc.mismatched), (2, 2));
-        let first = &r.calc.mismatches[0];
-        assert_eq!(first.cell, "Sheet1!B1");
-        assert_eq!(first.formula, "=SUM(A1:A2)");
-        assert_eq!((first.expected.clone(), first.actual.clone(), first.kind, first.primary), (n(7.0), n(6.0), "numeric", true));
-        assert!(!r.calc.mismatches[1].primary);
-        assert_eq!(r.calc.functions["SUM"], FnStat { checked: 1, mismatched: 1, primary: 1 });
-        assert_eq!(r.calc.functions["(no function)"], FnStat { checked: 1, mismatched: 1, primary: 0 });
-        assert!(!r.is_clean());
-    }
-
-    #[test]
-    fn errors_compare_by_kind() {
-        let wb = book(&[("A1", "=1/0", Value::Error(CellError::Div0)), ("A2", "=1/0", Value::Error(CellError::NA)), ("A3", "=1/0", n(0.0))]);
-        let r = check(&wb, &Options::default());
-        assert_eq!((r.calc.matched, r.calc.mismatched), (1, 2));
-        assert!(r.calc.mismatches.iter().all(|m| m.kind == "error"));
-        assert_eq!(r.calc.signatures.get("#N/A → #DIV/0!"), Some(&1));
-        assert_eq!(r.calc.signatures.get("number → #DIV/0!"), Some(&1));
-        assert!(values_match(&Value::Error(CellError::NA), &Value::Error(CellError::NA), 0.0));
-        assert!(!values_match(&Value::Error(CellError::NA), &Value::Error(CellError::Value), 0.0));
-    }
-
-    #[test]
-    fn numbers_compare_within_tolerance() {
-        assert!(values_match(&n(3.0000000001), &n(3.0), 1e-9));
-        assert!(!values_match(&n(3.0000000001), &n(3.0), 1e-12));
-        // Absolute near zero.
-        assert!(values_match(&n(1e-12), &n(0.0), 1e-9));
-        assert!(values_match(&n(1e12 + 1.0), &n(1e12), 1e-9));
-        assert!(!values_match(&n(0.0), &Value::Empty, 1.0));
-        assert!(!values_match(&Value::text("1"), &n(1.0), 1.0));
-        assert!(values_match(&Value::text("a"), &Value::text("a"), 0.0));
-        assert!(!values_match(&Value::text("a"), &Value::text("A"), 0.0));
-        assert!(!values_match(&Value::Bool(true), &n(1.0), 1.0));
-        let wb = book(&[("A1", "=1+2", n(3.0000000001))]);
-        assert_eq!(check(&wb, &Options::default()).calc.matched, 1);
-        assert_eq!(check(&wb, &Options { tolerance: 1e-12, ..Default::default() }).calc.mismatched, 1);
-    }
-
-    /// Business Central writes TRUE and FALSE as `<c><f>TRUE()</f><v>1</v></c>`, without `t="b"`:
-    /// the cache holds the right value under a number type, so it matches and is counted apart.
-    #[test]
-    fn booleans_cached_as_numbers_match_and_are_counted_apart() {
-        let wb = book(&[
-            ("A1", "=TRUE()", n(1.0)),
-            ("B1", "=FALSE()", n(0.0)),
-            ("C1", "=TRUE()", Value::Bool(true)),
-            ("D1", "=1=1", n(0.0)),
-            ("E1", "=TRUE()+0", n(1.0)),
-        ]);
-        let r = check(&wb, &Options::default());
-        assert_eq!((r.calc.checked, r.calc.matched, r.calc.mismatched), (5, 4, 1));
-        // A cached 0 for TRUE is still a mismatch, and a number result is compared as a number.
-        assert_eq!(r.calc.mismatches[0].cell, "Sheet1!D1");
-        assert_eq!(r.calc.signatures.get("number → bool"), Some(&1));
-        assert_eq!(r.calc.bool_as_number, 2);
-        let v = report_json(std::slice::from_ref(&r), &Options::default());
-        assert_eq!((v["files"][0]["calc"]["boolAsNumber"].clone(), v["totals"]["boolAsNumber"].clone()), (json!(2), json!(2)));
-        assert!(bool_cached_as_number(&n(1.0), &Value::Bool(true)));
-        assert!(!bool_cached_as_number(&n(1.0), &Value::Bool(false)));
-        assert!(!bool_cached_as_number(&n(2.0), &Value::Bool(true)));
-        assert!(!bool_cached_as_number(&Value::Bool(true), &n(1.0)));
-    }
-
-    #[test]
-    fn missing_cached_values_and_volatile_formulas_are_skipped() {
-        let wb =
-            book(&[("A1", "=1+1", Value::Empty), ("B1", "=NOW()", n(1.0)), ("B2", "=B1+1", n(2.0)), ("B3", "=CELL(\"filename\")", Value::text("x"))]);
-        let r = check(&wb, &Options::default());
-        assert_eq!((r.calc.formula_cells, r.calc.checked, r.calc.no_oracle, r.calc.volatile), (4, 0, 1, 3));
-    }
-
-    #[test]
-    fn full_calc_on_load_means_no_oracle() {
-        // A formula without a cached value makes GridCraft's writer flag the file
-        // `fullCalcOnLoad`, like libraries that store 0 for every formula: B1's wrong "cached"
-        // value must not count as a mismatch then.
-        let wb = book(&[("A1", "=1+1", Value::Empty), ("B1", "=2+2", n(0.0))]);
-        let bytes = gridcraft_engine::io::save_bytes(&wb, "t.xlsx").unwrap();
-        assert!(full_calc_on_load(&bytes));
-        let r = check_bytes("t.xlsx", &bytes, &Options::default());
-        assert!(r.calc.stale_cache);
-        assert_eq!((r.calc.checked, r.calc.no_oracle, r.calc.mismatched), (0, 2, 0));
-        let fresh = gridcraft_engine::io::save_bytes(&book(&[("B1", "=2+2", n(0.0))]), "t.xlsx").unwrap();
-        assert!(!full_calc_on_load(&fresh));
-        assert!(!full_calc_on_load(b"not a zip"));
-    }
-
-    #[test]
-    fn volatile_names_propagate() {
-        let mut wb = book(&[("A1", "=Stamp+1", n(1.0))]);
-        wb.names.push(gridcraft_engine::model::DefinedName {
-            name: "Stamp".into(),
-            scope: None,
-            formula: "TODAY()".into(),
-            comment: String::new(),
-            hidden: false,
-        });
-        assert!(volatile_names(&wb).contains("STAMP"));
-        assert_eq!(check(&wb, &Options::default()).calc.volatile, 1);
-    }
-
-    #[test]
-    fn round_trip_of_a_simple_book_is_clean() {
-        let mut wb = book(&[("A1", "2", n(2.0)), ("B1", "=A1*3", n(6.0)), ("A2", "x", Value::text("x"))]);
-        wb.sheet_mut(0).unwrap().merges.push(gridcraft_engine::core::RangeRef::parse("C1:D2").unwrap());
-        let source = gridcraft_engine::io::save_bytes(&wb, "t.xlsx").unwrap();
-        let rt = round_trip(&wb, &source, &Options::default());
-        assert_eq!(rt.error, None);
-        assert!(rt.is_clean(), "{rt:?}");
-        assert!(rt.categories.iter().any(|c| c.name == "package"));
-    }
-
-    #[test]
-    fn diff_detects_lost_features() {
-        let mut a = book(&[("A1", "2", n(2.0)), ("B1", "=A1*3", n(6.0))]);
-        a.sheet_mut(0).unwrap().merges.push(gridcraft_engine::core::RangeRef::parse("C1:D2").unwrap());
-        let mut b = a.clone();
-        let sh = b.sheet_mut(0).unwrap();
-        sh.merges.clear();
-        sh.set_cell(at("A1"), Cell::value(n(3.0)));
-        sh.set_cell(at("B1"), Cell::value(n(6.0)));
-        b.sheets.push(Arc::new(Sheet::new("Extra")));
-        let cats = diff_workbooks(&a, &b, &Options { max_report: 1, ..Default::default() });
-        let get = |name: &str| cats.iter().find(|c| c.name == name).unwrap();
-        assert_eq!(get("values").diffs, 1);
-        assert_eq!(get("values").examples, ["Sheet1!A1: 2 → 3"]);
-        assert_eq!(get("formulas").examples, ["Sheet1!B1: =A1*3 → "]);
-        assert_eq!(get("merges").examples, ["Sheet1: lost C1:D2"]);
-        assert_eq!(get("sheets").diffs, 1);
-        assert_eq!(get("tables").diffs, 0);
-    }
-
-    #[test]
-    fn diff_detects_changed_cond_format_rule() {
-        use gridcraft_engine::model::{CfRule, CfValueKind, Color, CondFormat};
-        let bar = |gradient: bool, priority: u32| CondFormat {
-            ranges: vec![gridcraft_engine::core::RangeRef::parse("A1").unwrap()],
-            rule: CfRule::DataBar { min: CfValueKind::Min, max: CfValueKind::Max, color: Color::Rgb(0x638EC6), gradient, show_value: true },
-            priority,
-            stop_if_true: false,
-        };
-        let with = |cf: CondFormat| {
-            let mut wb = book(&[("A1", "2", n(2.0))]);
-            wb.sheet_mut(0).unwrap().cond_formats.push(cf);
-            wb
-        };
-        let diffs =
-            |a: &Workbook, b: &Workbook| diff_workbooks(a, b, &Options::default()).into_iter().find(|c| c.name == "condFormats").unwrap().diffs;
-        assert_eq!(diffs(&with(bar(false, 1)), &with(bar(true, 1))), 1);
-        assert_eq!(diffs(&with(bar(true, 1)), &with(bar(true, 1))), 0);
-        assert_eq!(diffs(&with(bar(true, 1)), &with(bar(true, 5))), 0);
-    }
-
-    fn zip_of(parts: &[(&str, &str)]) -> Vec<u8> {
-        let mut z = zip::ZipWriter::new(Cursor::new(Vec::new()));
-        for (name, body) in parts {
-            z.start_file(*name, zip::write::SimpleFileOptions::default()).unwrap();
-            z.write_all(body.as_bytes()).unwrap();
-        }
-        z.finish().unwrap().into_inner()
-    }
-
-    #[test]
-    fn package_validation_finds_what_excel_would_repair() {
-        let bytes = zip_of(&[
-            (
-                "[Content_Types].xml",
-                r#"<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"><Default Extension="rels" ContentType="r"/><Override PartName="/xl/workbook.xml" ContentType="w"/><Override PartName="/xl/gone.xml" ContentType="g"/></Types>"#,
-            ),
-            ("_rels/.rels", r#"<Relationships><Relationship Id="rId1" Type="x/officeDocument" Target="xl/workbook.xml"/></Relationships>"#),
-            ("xl/workbook.xml", "<workbook/>"),
-            ("xl/styles.xml", "<styleSheet/>"),
-            (
-                "xl/_rels/workbook.xml.rels",
-                r#"<Relationships><Relationship Id="rId1" Type="x/styles" Target="styles.xml"/><Relationship Id="rId2" Type="x/worksheet" Target="worksheets/sheet1.xml"/><Relationship Id="rId2" Type="x/hyperlink" Target="https://example.com" TargetMode="External"/><Relationship Id="rId3" Type="x/theme" Target="/xl/../xl/styles.xml"/></Relationships>"#,
-            ),
-        ]);
-        let issues = validate_package(&bytes).unwrap();
-        assert_eq!(
-            issues,
-            [
-                "part xl/styles.xml has no content type",
-                "content type override for missing part /xl/gone.xml",
-                "xl/_rels/workbook.xml.rels: rId2 (worksheet) targets missing part xl/worksheets/sheet1.xml",
-                "xl/_rels/workbook.xml.rels: duplicate relationship id rId2",
-            ]
-        );
-        assert!(validate_package(b"not a zip").is_err());
-        let own = gridcraft_engine::io::save_bytes(&book(&[("A1", "=1", n(1.0))]), "t.xlsx").unwrap();
-        assert_eq!(validate_package(&own).unwrap(), Vec::<String>::new());
-    }
-
-    const WB_RELS: &str = "xl/_rels/workbook.xml.rels";
-    const SHEET_RELS: &str = "xl/worksheets/_rels/sheet1.xml.rels";
-    const MADE_UP: &str = r#"<Relationship Id="rId90" Type="http://example.com/relationships/madeUp" Target="madeUp.xml"/>"#;
-    /// Not empty: an empty part isn't a loss.
-    const MADE_UP_PART: (&str, &str) = ("xl/madeUp.xml", "<madeUp><item/></madeUp>");
-
-    /// `bytes` with relationships added to rels parts (created when missing) and `parts` added.
-    fn with_rels(bytes: &[u8], rels: &[(&str, &str)], parts: &[(&str, &str)]) -> Vec<u8> {
-        let mut src = zip::ZipArchive::new(Cursor::new(bytes)).unwrap();
-        let mut out = zip::ZipWriter::new(Cursor::new(Vec::new()));
-        let mut pending: Vec<(&str, &str)> = rels.to_vec();
-        for i in 0..src.len() {
-            let mut f = src.by_index(i).unwrap();
-            let name = f.name().to_string();
-            let mut body = String::new();
-            f.read_to_string(&mut body).unwrap();
-            if let Some(at) = pending.iter().position(|(r, _)| *r == name) {
-                body = body.replace("</Relationships>", &format!("{}</Relationships>", pending.remove(at).1));
-            }
-            out.start_file(name, zip::write::SimpleFileOptions::default()).unwrap();
-            out.write_all(body.as_bytes()).unwrap();
-        }
-        let created = pending.iter().map(|(r, extra)| {
-            (*r, format!(r#"<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">{extra}</Relationships>"#))
-        });
-        for (name, body) in created.collect::<Vec<_>>().iter().map(|(n, b)| (*n, b.as_str())).chain(parts.iter().copied()) {
-            out.start_file(name, zip::write::SimpleFileOptions::default()).unwrap();
-            out.write_all(body.as_bytes()).unwrap();
-        }
-        out.finish().unwrap().into_inner()
-    }
-
-    /// The `package` examples of checking `source`.
-    fn package_of(source: &[u8]) -> Vec<String> {
-        let r = check_bytes("t.xlsx", source, &Options::default());
-        r.round_trip.categories.iter().find(|c| c.name == "package").unwrap().examples.clone()
-    }
-
-    fn plain() -> Vec<u8> {
-        gridcraft_engine::io::save_bytes(&book(&[("A1", "1", n(1.0))]), "t.xlsx").unwrap()
-    }
-
-    #[test]
-    fn package_reports_relationship_kinds_the_output_lost() {
-        // A kind GridCraft doesn't know is dropped on save; a calculation chain is never written
-        // (Excel rebuilds it), so its absence isn't a loss.
-        let calc_chain = r#"<Relationship Id="rId91" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/calcChain" Target="calcChain.xml"/>"#;
-        let source = with_rels(&plain(), &[(WB_RELS, &format!("{MADE_UP}{calc_chain}"))], &[MADE_UP_PART, ("xl/calcChain.xml", "<calcChain/>")]);
-        assert_eq!(package_of(&source), ["lost relationship madeUp"]);
-        assert!(check_bytes("t.xlsx", &plain(), &Options::default()).round_trip.is_clean());
-    }
-
-    // In the three tests below the made-up kind stays lost, so the comparison is known to run.
-
-    #[test]
-    fn an_internal_link_written_as_a_relationship_is_not_a_loss() {
-        // openpyxl writes `#Sheet1!B2` as an external relationship; GridCraft writes `location`.
-        let link = r##"<Relationship Id="rId5" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/hyperlink" Target="#Sheet1!B2" TargetMode="External"/>"##;
-        let source = with_rels(&plain(), &[(WB_RELS, MADE_UP), (SHEET_RELS, link)], &[MADE_UP_PART]);
-        assert_eq!(package_of(&source), ["lost relationship madeUp"]);
-    }
-
-    #[test]
-    fn comments_without_a_comment_are_not_a_loss() {
-        let rels = r#"<Relationship Id="rId6" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/comments" Target="../comments1.xml"/><Relationship Id="rId7" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/vmlDrawing" Target="../drawings/vmlDrawing1.vml"/>"#;
-        let comments = r#"<comments xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"><authors><author>A</author></authors><commentList/></comments>"#;
-        let vml = r#"<xml xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office"><o:shapelayout><o:idmap data="1"/></o:shapelayout><v:shapetype id="_x0000_t202" path="m,l,21600r21600,l21600,xe"><v:path gradientshapeok="t"/></v:shapetype></xml>"#;
-        let source = with_rels(
-            &plain(),
-            &[(WB_RELS, MADE_UP), (SHEET_RELS, rels)],
-            &[MADE_UP_PART, ("xl/comments1.xml", comments), ("xl/drawings/vmlDrawing1.vml", vml)],
-        );
-        assert_eq!(package_of(&source), ["lost relationship madeUp"]);
-    }
-
-    #[test]
-    fn empty_drawings_and_person_lists_are_not_a_loss() {
-        let drawing = r#"<Relationship Id="rId8" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/drawing" Target="../drawings/drawing1.xml"/>"#;
-        let person =
-            r#"<Relationship Id="rId92" Type="http://schemas.microsoft.com/office/2017/10/relationships/person" Target="persons/person.xml"/>"#;
-        let source = with_rels(
-            &plain(),
-            &[(WB_RELS, &format!("{MADE_UP}{person}")), (SHEET_RELS, drawing)],
-            &[
-                MADE_UP_PART,
-                ("xl/drawings/drawing1.xml", r#"<xdr:wsDr xmlns:xdr="http://schemas.openxmlformats.org/drawingml/2006/spreadsheetDrawing"/>"#),
-                ("xl/persons/person.xml", r#"<personList xmlns="http://schemas.microsoft.com/office/spreadsheetml/2018/threadedcomments"/>"#),
-            ],
-        );
-        assert_eq!(package_of(&source), ["lost relationship madeUp"]);
-    }
-
-    #[test]
-    fn json_lists_warning_messages() {
-        let with = FileReport { path: "a.ods".into(), warnings: vec!["ODS data-only import".into()], ..Default::default() };
-        let without = FileReport { path: "b.xlsx".into(), ..Default::default() };
-        let v = report_json(&[with, without], &Options::default());
-        assert_eq!(v["files"][0]["warnings"], json!(["ODS data-only import"]));
-        assert_eq!(v["files"][1]["warnings"], json!([]));
-    }
-
-    #[test]
-    fn unopenable_files_are_reported() {
-        let r = check_bytes("broken.xlsx", b"PK\x03\x04 not really", &Options::default());
-        assert!(r.error.is_some());
-        assert!(!r.is_clean());
-    }
-
-    #[test]
-    fn json_schema_keys() {
-        let wb = book(&[("A1", "=1+1", n(3.0))]);
-        let reports = vec![check(&wb, &Options::default()), check_bytes("bad.xlsx", b"", &Options::default())];
-        let v = report_json(&reports, &Options::default());
-        let keys = |v: &Json| v.as_object().unwrap().keys().cloned().collect::<BTreeSet<String>>();
-        let set = |k: &[&str]| k.iter().map(|s| s.to_string()).collect::<BTreeSet<String>>();
-        assert_eq!(keys(&v), set(&["schema", "tolerance", "files", "totals", "functions", "signatures"]));
-        assert_eq!(v["schema"], SCHEMA);
-        let f = &v["files"][0];
-        assert_eq!(keys(f), set(&["path", "opened", "error", "warnings", "calc", "roundTrip"]));
-        assert_eq!(
-            keys(&f["calc"]),
-            set(&[
-                "formulaCells",
-                "checked",
-                "matched",
-                "mismatched",
-                "noOracle",
-                "staleCache",
-                "volatile",
-                "boolAsNumber",
-                "mismatches",
-                "functions",
-                "signatures"
-            ])
-        );
-        assert_eq!(f["calc"]["signatures"], json!({"number → number": 1}));
-        assert_eq!(keys(&f["calc"]["mismatches"][0]), set(&["cell", "formula", "expected", "actual", "kind", "functions", "primary"]));
-        assert_eq!(f["calc"]["mismatches"][0]["expected"], json!(3.0));
-        assert_eq!(keys(&f["roundTrip"]), set(&["error", "differing", "categories"]));
-        assert_eq!(
-            keys(&f["roundTrip"]["categories"]),
-            set(&[
-                "sheets",
-                "values",
-                "formulas",
-                "numFmts",
-                "merges",
-                "names",
-                "tables",
-                "condFormats",
-                "validations",
-                "charts",
-                "comments",
-                "hyperlinks",
-                "pivots",
-                "package"
-            ])
-        );
-        assert_eq!(keys(&f["roundTrip"]["categories"]["values"]), set(&["equal", "diffs", "examples"]));
-        assert_eq!(v["files"][1]["opened"], json!(false));
-        assert_eq!(
-            keys(&v["totals"]),
-            set(&[
-                "files",
-                "opened",
-                "failedToOpen",
-                "formulaCells",
-                "checked",
-                "matched",
-                "mismatched",
-                "noOracle",
-                "volatile",
-                "boolAsNumber",
-                "roundTripFailed",
-                "roundTripDiffering",
-                "categoriesDiffering"
-            ])
-        );
-        assert_eq!(keys(&v["functions"][0]), set(&["name", "checked", "mismatched", "primary"]));
-    }
-}
+mod tests;
diff --git a/apps/gridcraft-cli/src/check/tests.rs b/apps/gridcraft-cli/src/check/tests.rs
new file mode 100644
index 000000000..f1df04670
--- /dev/null
+++ b/apps/gridcraft-cli/src/check/tests.rs
@@ -0,0 +1,451 @@
+#![allow(clippy::unwrap_used)]
+use std::io::Write as _;
+use std::sync::Arc;
+
+use gridcraft_engine::model::Formula;
+
+use super::*;
+
+#[test]
+fn discovery_reports_a_directory_read_error() {
+    let path = std::env::temp_dir().join(format!("gridcraft-check-not-a-directory-{}", std::process::id()));
+    std::fs::write(&path, "not a directory").unwrap();
+    let mut discovery = Discovery::default();
+    let mut seen = std::collections::HashSet::new();
+    assert!(walk(&path, 0, &mut discovery, &mut seen));
+    assert!(discovery.files.is_empty());
+    assert_eq!(discovery.failures.len(), 1);
+    assert_eq!(discovery.failures[0].path, path.to_string_lossy());
+    assert!(discovery.failures[0].error.as_ref().unwrap().contains("cannot read directory"));
+    let _ = std::fs::remove_file(path);
+}
+
+#[test]
+fn discovery_reports_omissions_only_after_the_file_limit() {
+    let mut discovery = Discovery { files: vec![PathBuf::from("book.xlsx"); MAX_FILES - 1], ..Default::default() };
+    assert!(discovery.add_file(PathBuf::from("last.xlsx")));
+    assert!(discovery.failures.is_empty());
+    assert!(!discovery.add_file(PathBuf::from("omitted.xlsx")));
+    assert_eq!(discovery.files.len(), MAX_FILES);
+    assert_eq!(discovery.failures[0].path, "omitted.xlsx");
+    assert!(discovery.failures[0].error.as_ref().unwrap().contains("file limit"));
+}
+
+fn at(a1: &str) -> CellRef {
+    CellRef::parse(a1).unwrap()
+}
+
+/// A workbook whose cells are `(A1, input, cached value)`: an input starting with `=` is a
+/// formula with that cached value, anything else a constant.
+fn book(cells: &[(&str, &str, Value)]) -> Workbook {
+    let mut wb = Workbook::new();
+    let sh = wb.sheet_mut(0).unwrap();
+    for (a1, input, cached) in cells {
+        let cell = if input.starts_with('=') {
+            Cell { value: cached.clone(), formula: Some(Arc::new(Formula::new(input))), ..Default::default() }
+        } else {
+            Cell::value(cached.clone())
+        };
+        sh.set_cell(at(a1), cell);
+    }
+    wb
+}
+
+fn check(wb: &Workbook, opts: &Options) -> FileReport {
+    let bytes = gridcraft_engine::io::save_bytes(wb, "t.xlsx").unwrap();
+    check_bytes("t.xlsx", &bytes, opts)
+}
+
+fn n(x: f64) -> Value {
+    Value::number(x)
+}
+
+#[test]
+fn matching_cached_values_pass() {
+    let wb = book(&[("A1", "2", n(2.0)), ("B1", "=A1*3", n(6.0)), ("C1", "=A1&\"x\"", Value::text("2x")), ("D1", "=A1>1", Value::Bool(true))]);
+    let r = check(&wb, &Options::default());
+    assert_eq!(r.error, None);
+    assert_eq!((r.calc.formula_cells, r.calc.checked, r.calc.matched, r.calc.mismatched), (3, 3, 3, 0));
+    assert!(r.is_clean(), "{r:?}");
+}
+
+#[test]
+fn wrong_cached_value_is_a_mismatch_and_ranks_its_function() {
+    // Excel "said" SUM gives 7; GridCraft computes 6. C1 reads B1 and is consistent with
+    // Excel's 7, so it mismatches too, but only as a downstream effect.
+    let wb = book(&[("A1", "2", n(2.0)), ("A2", "4", n(4.0)), ("B1", "=SUM(A1:A2)", n(7.0)), ("C1", "=B1+1", n(8.0))]);
+    let r = check(&wb, &Options::default());
+    assert_eq!((r.calc.checked, r.calc.mismatched), (2, 2));
+    let first = &r.calc.mismatches[0];
+    assert_eq!(first.cell, "Sheet1!B1");
+    assert_eq!(first.formula, "=SUM(A1:A2)");
+    assert_eq!((first.expected.clone(), first.actual.clone(), first.kind, first.primary), (n(7.0), n(6.0), "numeric", true));
+    assert!(!r.calc.mismatches[1].primary);
+    assert_eq!(r.calc.functions["SUM"], FnStat { checked: 1, mismatched: 1, primary: 1 });
+    assert_eq!(r.calc.functions["(no function)"], FnStat { checked: 1, mismatched: 1, primary: 0 });
+    assert!(!r.is_clean());
+}
+
+#[test]
+fn errors_compare_by_kind() {
+    let wb = book(&[("A1", "=1/0", Value::Error(CellError::Div0)), ("A2", "=1/0", Value::Error(CellError::NA)), ("A3", "=1/0", n(0.0))]);
+    let r = check(&wb, &Options::default());
+    assert_eq!((r.calc.matched, r.calc.mismatched), (1, 2));
+    assert!(r.calc.mismatches.iter().all(|m| m.kind == "error"));
+    assert_eq!(r.calc.signatures.get("#N/A → #DIV/0!"), Some(&1));
+    assert_eq!(r.calc.signatures.get("number → #DIV/0!"), Some(&1));
+    assert!(values_match(&Value::Error(CellError::NA), &Value::Error(CellError::NA), 0.0));
+    assert!(!values_match(&Value::Error(CellError::NA), &Value::Error(CellError::Value), 0.0));
+}
+
+#[test]
+fn numbers_compare_within_tolerance() {
+    assert!(values_match(&n(3.0000000001), &n(3.0), 1e-9));
+    assert!(!values_match(&n(3.0000000001), &n(3.0), 1e-12));
+    // Absolute near zero.
+    assert!(values_match(&n(1e-12), &n(0.0), 1e-9));
+    assert!(values_match(&n(1e12 + 1.0), &n(1e12), 1e-9));
+    assert!(!values_match(&n(0.0), &Value::Empty, 1.0));
+    assert!(!values_match(&Value::text("1"), &n(1.0), 1.0));
+    assert!(values_match(&Value::text("a"), &Value::text("a"), 0.0));
+    assert!(!values_match(&Value::text("a"), &Value::text("A"), 0.0));
+    assert!(!values_match(&Value::Bool(true), &n(1.0), 1.0));
+    let wb = book(&[("A1", "=1+2", n(3.0000000001))]);
+    assert_eq!(check(&wb, &Options::default()).calc.matched, 1);
+    assert_eq!(check(&wb, &Options { tolerance: 1e-12, ..Default::default() }).calc.mismatched, 1);
+}
+
+/// Business Central writes TRUE and FALSE as `<c><f>TRUE()</f><v>1</v></c>`, without `t="b"`:
+/// the cache holds the right value under a number type, so it matches and is counted apart.
+#[test]
+fn booleans_cached_as_numbers_match_and_are_counted_apart() {
+    let wb = book(&[
+        ("A1", "=TRUE()", n(1.0)),
+        ("B1", "=FALSE()", n(0.0)),
+        ("C1", "=TRUE()", Value::Bool(true)),
+        ("D1", "=1=1", n(0.0)),
+        ("E1", "=TRUE()+0", n(1.0)),
+    ]);
+    let r = check(&wb, &Options::default());
+    assert_eq!((r.calc.checked, r.calc.matched, r.calc.mismatched), (5, 4, 1));
+    // A cached 0 for TRUE is still a mismatch, and a number result is compared as a number.
+    assert_eq!(r.calc.mismatches[0].cell, "Sheet1!D1");
+    assert_eq!(r.calc.signatures.get("number → bool"), Some(&1));
+    assert_eq!(r.calc.bool_as_number, 2);
+    let v = report_json(std::slice::from_ref(&r), &Options::default());
+    assert_eq!((v["files"][0]["calc"]["boolAsNumber"].clone(), v["totals"]["boolAsNumber"].clone()), (json!(2), json!(2)));
+    assert!(bool_cached_as_number(&n(1.0), &Value::Bool(true)));
+    assert!(!bool_cached_as_number(&n(1.0), &Value::Bool(false)));
+    assert!(!bool_cached_as_number(&n(2.0), &Value::Bool(true)));
+    assert!(!bool_cached_as_number(&Value::Bool(true), &n(1.0)));
+}
+
+#[test]
+fn missing_cached_values_and_volatile_formulas_are_skipped() {
+    let wb =
+        book(&[("A1", "=1+1", Value::Empty), ("B1", "=NOW()", n(1.0)), ("B2", "=B1+1", n(2.0)), ("B3", "=CELL(\"filename\")", Value::text("x"))]);
+    let r = check(&wb, &Options::default());
+    assert_eq!((r.calc.formula_cells, r.calc.checked, r.calc.no_oracle, r.calc.volatile), (4, 0, 1, 3));
+}
+
+#[test]
+fn full_calc_on_load_means_no_oracle() {
+    // A formula without a cached value makes GridCraft's writer flag the file
+    // `fullCalcOnLoad`, like libraries that store 0 for every formula: B1's wrong "cached"
+    // value must not count as a mismatch then.
+    let wb = book(&[("A1", "=1+1", Value::Empty), ("B1", "=2+2", n(0.0))]);
+    let bytes = gridcraft_engine::io::save_bytes(&wb, "t.xlsx").unwrap();
+    assert!(full_calc_on_load(&bytes));
+    let r = check_bytes("t.xlsx", &bytes, &Options::default());
+    assert!(r.calc.stale_cache);
+    assert_eq!((r.calc.checked, r.calc.no_oracle, r.calc.mismatched), (0, 2, 0));
+    let fresh = gridcraft_engine::io::save_bytes(&book(&[("B1", "=2+2", n(0.0))]), "t.xlsx").unwrap();
+    assert!(!full_calc_on_load(&fresh));
+    assert!(!full_calc_on_load(b"not a zip"));
+}
+
+#[test]
+fn volatile_names_propagate() {
+    let mut wb = book(&[("A1", "=Stamp+1", n(1.0))]);
+    wb.names.push(gridcraft_engine::model::DefinedName {
+        name: "Stamp".into(),
+        scope: None,
+        formula: "TODAY()".into(),
+        comment: String::new(),
+        hidden: false,
+    });
+    assert!(volatile_names(&wb).contains("STAMP"));
+    assert_eq!(check(&wb, &Options::default()).calc.volatile, 1);
+}
+
+#[test]
+fn round_trip_of_a_simple_book_is_clean() {
+    let mut wb = book(&[("A1", "2", n(2.0)), ("B1", "=A1*3", n(6.0)), ("A2", "x", Value::text("x"))]);
+    wb.sheet_mut(0).unwrap().merges.push(gridcraft_engine::core::RangeRef::parse("C1:D2").unwrap());
+    let source = gridcraft_engine::io::save_bytes(&wb, "t.xlsx").unwrap();
+    let rt = round_trip(&wb, &source, &Options::default());
+    assert_eq!(rt.error, None);
+    assert!(rt.is_clean(), "{rt:?}");
+    assert!(rt.categories.iter().any(|c| c.name == "package"));
+}
+
+#[test]
+fn diff_detects_lost_features() {
+    let mut a = book(&[("A1", "2", n(2.0)), ("B1", "=A1*3", n(6.0))]);
+    a.sheet_mut(0).unwrap().merges.push(gridcraft_engine::core::RangeRef::parse("C1:D2").unwrap());
+    let mut b = a.clone();
+    let sh = b.sheet_mut(0).unwrap();
+    sh.merges.clear();
+    sh.set_cell(at("A1"), Cell::value(n(3.0)));
+    sh.set_cell(at("B1"), Cell::value(n(6.0)));
+    b.sheets.push(Arc::new(Sheet::new("Extra")));
+    let cats = diff_workbooks(&a, &b, &Options { max_report: 1, ..Default::default() });
+    let get = |name: &str| cats.iter().find(|c| c.name == name).unwrap();
+    assert_eq!(get("values").diffs, 1);
+    assert_eq!(get("values").examples, ["Sheet1!A1: 2 → 3"]);
+    assert_eq!(get("formulas").examples, ["Sheet1!B1: =A1*3 → "]);
+    assert_eq!(get("merges").examples, ["Sheet1: lost C1:D2"]);
+    assert_eq!(get("sheets").diffs, 1);
+    assert_eq!(get("tables").diffs, 0);
+}
+
+#[test]
+fn diff_detects_changed_cond_format_rule() {
+    use gridcraft_engine::model::{CfRule, CfValueKind, Color, CondFormat};
+    let bar = |gradient: bool, priority: u32| CondFormat {
+        ranges: vec![gridcraft_engine::core::RangeRef::parse("A1").unwrap()],
+        rule: CfRule::DataBar { min: CfValueKind::Min, max: CfValueKind::Max, color: Color::Rgb(0x638EC6), gradient, show_value: true },
+        priority,
+        stop_if_true: false,
+    };
+    let with = |cf: CondFormat| {
+        let mut wb = book(&[("A1", "2", n(2.0))]);
+        wb.sheet_mut(0).unwrap().cond_formats.push(cf);
+        wb
+    };
+    let diffs =
+        |a: &Workbook, b: &Workbook| diff_workbooks(a, b, &Options::default()).into_iter().find(|c| c.name == "condFormats").unwrap().diffs;
+    assert_eq!(diffs(&with(bar(false, 1)), &with(bar(true, 1))), 1);
+    assert_eq!(diffs(&with(bar(true, 1)), &with(bar(true, 1))), 0);
+    assert_eq!(diffs(&with(bar(true, 1)), &with(bar(true, 5))), 0);
+}
+
+fn zip_of(parts: &[(&str, &str)]) -> Vec<u8> {
+    let mut z = zip::ZipWriter::new(Cursor::new(Vec::new()));
+    for (name, body) in parts {
+        z.start_file(*name, zip::write::SimpleFileOptions::default()).unwrap();
+        z.write_all(body.as_bytes()).unwrap();
+    }
+    z.finish().unwrap().into_inner()
+}
+
+#[test]
+fn package_validation_finds_what_excel_would_repair() {
+    let bytes = zip_of(&[
+        (
+            "[Content_Types].xml",
+            r#"<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"><Default Extension="rels" ContentType="r"/><Override PartName="/xl/workbook.xml" ContentType="w"/><Override PartName="/xl/gone.xml" ContentType="g"/></Types>"#,
+        ),
+        ("_rels/.rels", r#"<Relationships><Relationship Id="rId1" Type="x/officeDocument" Target="xl/workbook.xml"/></Relationships>"#),
+        ("xl/workbook.xml", "<workbook/>"),
+        ("xl/styles.xml", "<styleSheet/>"),
+        (
+            "xl/_rels/workbook.xml.rels",
+            r#"<Relationships><Relationship Id="rId1" Type="x/styles" Target="styles.xml"/><Relationship Id="rId2" Type="x/worksheet" Target="worksheets/sheet1.xml"/><Relationship Id="rId2" Type="x/hyperlink" Target="https://example.com" TargetMode="External"/><Relationship Id="rId3" Type="x/theme" Target="/xl/../xl/styles.xml"/></Relationships>"#,
+        ),
+    ]);
+    let issues = validate_package(&bytes).unwrap();
+    assert_eq!(
+        issues,
+        [
+            "part xl/styles.xml has no content type",
+            "content type override for missing part /xl/gone.xml",
+            "xl/_rels/workbook.xml.rels: rId2 (worksheet) targets missing part xl/worksheets/sheet1.xml",
+            "xl/_rels/workbook.xml.rels: duplicate relationship id rId2",
+        ]
+    );
+    assert!(validate_package(b"not a zip").is_err());
+    let own = gridcraft_engine::io::save_bytes(&book(&[("A1", "=1", n(1.0))]), "t.xlsx").unwrap();
+    assert_eq!(validate_package(&own).unwrap(), Vec::<String>::new());
+}
+
+const WB_RELS: &str = "xl/_rels/workbook.xml.rels";
+const SHEET_RELS: &str = "xl/worksheets/_rels/sheet1.xml.rels";
+const MADE_UP: &str = r#"<Relationship Id="rId90" Type="http://example.com/relationships/madeUp" Target="madeUp.xml"/>"#;
+/// Not empty: an empty part isn't a loss.
+const MADE_UP_PART: (&str, &str) = ("xl/madeUp.xml", "<madeUp><item/></madeUp>");
+
+/// `bytes` with relationships added to rels parts (created when missing) and `parts` added.
+fn with_rels(bytes: &[u8], rels: &[(&str, &str)], parts: &[(&str, &str)]) -> Vec<u8> {
+    let mut src = zip::ZipArchive::new(Cursor::new(bytes)).unwrap();
+    let mut out = zip::ZipWriter::new(Cursor::new(Vec::new()));
+    let mut pending: Vec<(&str, &str)> = rels.to_vec();
+    for i in 0..src.len() {
+        let mut f = src.by_index(i).unwrap();
+        let name = f.name().to_string();
+        let mut body = String::new();
+        f.read_to_string(&mut body).unwrap();
+        if let Some(at) = pending.iter().position(|(r, _)| *r == name) {
+            body = body.replace("</Relationships>", &format!("{}</Relationships>", pending.remove(at).1));
+        }
+        out.start_file(name, zip::write::SimpleFileOptions::default()).unwrap();
+        out.write_all(body.as_bytes()).unwrap();
+    }
+    let created = pending.iter().map(|(r, extra)| {
+        (*r, format!(r#"<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">{extra}</Relationships>"#))
+    });
+    for (name, body) in created.collect::<Vec<_>>().iter().map(|(n, b)| (*n, b.as_str())).chain(parts.iter().copied()) {
+        out.start_file(name, zip::write::SimpleFileOptions::default()).unwrap();
+        out.write_all(body.as_bytes()).unwrap();
+    }
+    out.finish().unwrap().into_inner()
+}
+
+/// The `package` examples of checking `source`.
+fn package_of(source: &[u8]) -> Vec<String> {
+    let r = check_bytes("t.xlsx", source, &Options::default());
+    r.round_trip.categories.iter().find(|c| c.name == "package").unwrap().examples.clone()
+}
+
+fn plain() -> Vec<u8> {
+    gridcraft_engine::io::save_bytes(&book(&[("A1", "1", n(1.0))]), "t.xlsx").unwrap()
+}
+
+#[test]
+fn package_reports_relationship_kinds_the_output_lost() {
+    // A kind GridCraft doesn't know is dropped on save; a calculation chain is never written
+    // (Excel rebuilds it), so its absence isn't a loss.
+    let calc_chain = r#"<Relationship Id="rId91" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/calcChain" Target="calcChain.xml"/>"#;
+    let source = with_rels(&plain(), &[(WB_RELS, &format!("{MADE_UP}{calc_chain}"))], &[MADE_UP_PART, ("xl/calcChain.xml", "<calcChain/>")]);
+    assert_eq!(package_of(&source), ["lost relationship madeUp"]);
+    assert!(check_bytes("t.xlsx", &plain(), &Options::default()).round_trip.is_clean());
+}
+
+// In the three tests below the made-up kind stays lost, so the comparison is known to run.
+
+#[test]
+fn an_internal_link_written_as_a_relationship_is_not_a_loss() {
+    // openpyxl writes `#Sheet1!B2` as an external relationship; GridCraft writes `location`.
+    let link = r##"<Relationship Id="rId5" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/hyperlink" Target="#Sheet1!B2" TargetMode="External"/>"##;
+    let source = with_rels(&plain(), &[(WB_RELS, MADE_UP), (SHEET_RELS, link)], &[MADE_UP_PART]);
+    assert_eq!(package_of(&source), ["lost relationship madeUp"]);
+}
+
+#[test]
+fn comments_without_a_comment_are_not_a_loss() {
+    let rels = r#"<Relationship Id="rId6" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/comments" Target="../comments1.xml"/><Relationship Id="rId7" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/vmlDrawing" Target="../drawings/vmlDrawing1.vml"/>"#;
+    let comments = r#"<comments xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"><authors><author>A</author></authors><commentList/></comments>"#;
+    let vml = r#"<xml xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office"><o:shapelayout><o:idmap data="1"/></o:shapelayout><v:shapetype id="_x0000_t202" path="m,l,21600r21600,l21600,xe"><v:path gradientshapeok="t"/></v:shapetype></xml>"#;
+    let source = with_rels(
+        &plain(),
+        &[(WB_RELS, MADE_UP), (SHEET_RELS, rels)],
+        &[MADE_UP_PART, ("xl/comments1.xml", comments), ("xl/drawings/vmlDrawing1.vml", vml)],
+    );
+    assert_eq!(package_of(&source), ["lost relationship madeUp"]);
+}
+
+#[test]
+fn empty_drawings_and_person_lists_are_not_a_loss() {
+    let drawing = r#"<Relationship Id="rId8" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/drawing" Target="../drawings/drawing1.xml"/>"#;
+    let person =
+        r#"<Relationship Id="rId92" Type="http://schemas.microsoft.com/office/2017/10/relationships/person" Target="persons/person.xml"/>"#;
+    let source = with_rels(
+        &plain(),
+        &[(WB_RELS, &format!("{MADE_UP}{person}")), (SHEET_RELS, drawing)],
+        &[
+            MADE_UP_PART,
+            ("xl/drawings/drawing1.xml", r#"<xdr:wsDr xmlns:xdr="http://schemas.openxmlformats.org/drawingml/2006/spreadsheetDrawing"/>"#),
+            ("xl/persons/person.xml", r#"<personList xmlns="http://schemas.microsoft.com/office/spreadsheetml/2018/threadedcomments"/>"#),
+        ],
+    );
+    assert_eq!(package_of(&source), ["lost relationship madeUp"]);
+}
+
+#[test]
+fn json_lists_warning_messages() {
+    let with = FileReport { path: "a.ods".into(), warnings: vec!["ODS data-only import".into()], ..Default::default() };
+    let without = FileReport { path: "b.xlsx".into(), ..Default::default() };
+    let v = report_json(&[with, without], &Options::default());
+    assert_eq!(v["files"][0]["warnings"], json!(["ODS data-only import"]));
+    assert_eq!(v["files"][1]["warnings"], json!([]));
+}
+
+#[test]
+fn unopenable_files_are_reported() {
+    let r = check_bytes("broken.xlsx", b"PK\x03\x04 not really", &Options::default());
+    assert!(r.error.is_some());
+    assert!(!r.is_clean());
+}
+
+#[test]
+fn json_schema_keys() {
+    let wb = book(&[("A1", "=1+1", n(3.0))]);
+    let reports = vec![check(&wb, &Options::default()), check_bytes("bad.xlsx", b"", &Options::default())];
+    let v = report_json(&reports, &Options::default());
+    let keys = |v: &Json| v.as_object().unwrap().keys().cloned().collect::<BTreeSet<String>>();
+    let set = |k: &[&str]| k.iter().map(|s| s.to_string()).collect::<BTreeSet<String>>();
+    assert_eq!(keys(&v), set(&["schema", "tolerance", "files", "totals", "functions", "signatures"]));
+    assert_eq!(v["schema"], SCHEMA);
+    let f = &v["files"][0];
+    assert_eq!(keys(f), set(&["path", "opened", "error", "warnings", "calc", "roundTrip"]));
+    assert_eq!(
+        keys(&f["calc"]),
+        set(&[
+            "formulaCells",
+            "checked",
+            "matched",
+            "mismatched",
+            "noOracle",
+            "staleCache",
+            "volatile",
+            "boolAsNumber",
+            "mismatches",
+            "functions",
+            "signatures"
+        ])
+    );
+    assert_eq!(f["calc"]["signatures"], json!({"number → number": 1}));
+    assert_eq!(keys(&f["calc"]["mismatches"][0]), set(&["cell", "formula", "expected", "actual", "kind", "functions", "primary"]));
+    assert_eq!(f["calc"]["mismatches"][0]["expected"], json!(3.0));
+    assert_eq!(keys(&f["roundTrip"]), set(&["error", "differing", "categories"]));
+    assert_eq!(
+        keys(&f["roundTrip"]["categories"]),
+        set(&[
+            "sheets",
+            "values",
+            "formulas",
+            "numFmts",
+            "merges",
+            "names",
+            "tables",
+            "condFormats",
+            "validations",
+            "charts",
+            "comments",
+            "hyperlinks",
+            "pivots",
+            "package"
+        ])
+    );
+    assert_eq!(keys(&f["roundTrip"]["categories"]["values"]), set(&["equal", "diffs", "examples"]));
+    assert_eq!(v["files"][1]["opened"], json!(false));
+    assert_eq!(
+        keys(&v["totals"]),
+        set(&[
+            "files",
+            "opened",
+            "failedToOpen",
+            "formulaCells",
+            "checked",
+            "matched",
+            "mismatched",
+            "noOracle",
+            "volatile",
+            "boolAsNumber",
+            "roundTripFailed",
+            "roundTripDiffering",
+            "categoriesDiffering"
+        ])
+    );
+    assert_eq!(keys(&v["functions"][0]), set(&["name", "checked", "mismatched", "primary"]));
+}