Merge pull request #143 from fiddlerwoaroof/fix/a36c-count-exact

test(core): count_aggregation asserts the count, not that it is at least one (improvise-a36c)

context/test-evidence/core.md

@@ -1217,3 +1217,29 @@ view a fresh workbook creates. Making `Workbook::create_view` refuse or rename
 a name it already holds passes this test and breaks records mode, because both
 rebuilders depend on the replacement — which is why the fix is a helper beside
 `create_view` and not a change to it.
+
+### model::types::formula_tests::count_aggregation
+
+improvise-a36c. The test asserted `val >= 1.0` for `COUNT(Sales)` at
+`Region=East`, where the fixture's answer is exactly `1.0` — so every inflated
+count cleared the bar. The ticket's own fault injection (`values.len() + 999.0`
+in `eval_agg`) is not the worst case: it fails one *other* test,
+`model::types::agg_helper_tests::eval_agg_over_no_rows_is_zero_only_where_an_identity_exists`,
+which sees the empty case move from `0` to `999`. Preserve the empty case
+(`if values.is_empty() { 0.0 } else { len + 999.0 }`) and the **entire
+workspace of 1699 tests passes** while `COUNT` over any non-empty set is wrong
+by 999. That measurement, not the ticket's, is what this entry exists to record:
+the only thing standing between a wrong `COUNT` and a green suite was a check on
+the identity element, which is the one input `COUNT` gets right by accident.
+
+Two assertions, because one does not separate the neighbouring question.
+`assert_eq!(at East, 1.0)` answers *is the count inflated* — it fails the
+`+999` rival at `left: Some(1000.0)`. It does **not** answer *does `COUNT` count
+anything*: a `Count` arm returning a constant `1.0` satisfies it, and at a
+fixture whose expected value is `1` that rival is invisible by construction.
+The second assertion, `COUNT` unscoped over all three regions being `3.0`,
+is what fails it, at `left: Some(1.0)`. Both rivals were injected and both fail,
+at different assertions — the first at the East count, the second at the total.
+
+The fixture is deliberately asymmetric: one matching cell under the scoped key
+and three under the unscoped one, so no single constant can satisfy both.

crates/improvise-core/src/model/types.rs

@@ -1765,11 +1765,12 @@ mod formula_tests {
             );
         }
         m.add_formula(parse_formula("Count = COUNT(Sales)", "_Measure").unwrap());
-        let val = m
-            .evaluate(&coord(&[("_Measure", "Count"), ("Region", "East")]))
-            .and_then(|v| v.as_f64())
-            .unwrap();
-        assert!(val >= 1.0);
+        let count_at = |k: CellKey| m.evaluate(&k).and_then(|v| v.as_f64());
+        assert_eq!(
+            count_at(coord(&[("_Measure", "Count"), ("Region", "East")])),
+            Some(1.0)
+        );
+        assert_eq!(count_at(coord(&[("_Measure", "Count")])), Some(3.0));
     }
 
     #[test]