test: extend DateOnly/TimeOnly type-mapping coverage (+7 tests, 317→324)

Add the tests that were missing after PRs #393 and #394 landed:

* required date → DateOnly when useDateOnly=true
* optional date → Option<DateOnly> when useDateOnly=true
* optional time → Option<TimeOnly> when useDateOnly=true
* PreferNullable+useDateOnly: optional DateOnly → Nullable<DateOnly>
* PreferNullable+useDateOnly: required DateOnly stays unwrapped
* PreferNullable+useDateOnly: optional TimeOnly → Nullable<TimeOnly>
* PreferNullable+useDateOnly: required TimeOnly stays unwrapped

Also expose compilePropertyTypeWithNullableAndDateOnly helper in
Schema.TestHelpers for the PreferNullable×useDateOnly combination.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

tests/SwaggerProvider.Tests/Schema.TestHelpers.fs

@@ -101,3 +101,7 @@ let compilePropertyTypeWith (provideNullable: bool) (propYaml: string) (required
 /// Compile a minimal v3 schema where date/time formats map to DateOnly/TimeOnly types.
 let compilePropertyTypeWithDateOnly (propYaml: string) (required: bool) : Type =
     compilePropertyTypeWithOptions false true propYaml required
+
+/// Compile a minimal v3 schema with both PreferNullable and useDateOnly options enabled.
+let compilePropertyTypeWithNullableAndDateOnly (propYaml: string) (required: bool) : Type =
+    compilePropertyTypeWithOptions true true propYaml required

tests/SwaggerProvider.Tests/Schema.TypeMappingTests.fs

@@ -59,6 +59,13 @@ let ``required string date format maps to DateTimeOffset``() =
 
     ty |> shouldEqual typeof<DateTimeOffset>
 
+[<Fact>]
+let ``required string date format maps to DateOnly when useDateOnly is true``() =
+    let ty =
+        compilePropertyTypeWithDateOnly "          type: string\n          format: date\n" true
+
+    ty |> shouldEqual typeof<DateOnly>
+
 [<Fact>]
 let ``required string time format falls back to string when useDateOnly is false``() =
     // The test helper compiles with useDateOnly=false, so TimeOnly is not used
@@ -136,6 +143,22 @@ let ``optional DateTimeOffset maps to Option<DateTimeOffset>``() =
     ty
     |> shouldEqual(typedefof<Option<_>>.MakeGenericType(typeof<DateTimeOffset>))
 
+[<Fact>]
+let ``optional DateOnly maps to Option<DateOnly> when useDateOnly is true``() =
+    let ty =
+        compilePropertyTypeWithDateOnly "          type: string\n          format: date\n" false
+
+    ty
+    |> shouldEqual(typedefof<Option<_>>.MakeGenericType(typeof<DateOnly>))
+
+[<Fact>]
+let ``optional TimeOnly maps to Option<TimeOnly> when useDateOnly is true``() =
+    let ty =
+        compilePropertyTypeWithDateOnly "          type: string\n          format: time\n" false
+
+    ty
+    |> shouldEqual(typedefof<Option<_>>.MakeGenericType(typeof<TimeOnly>))
+
 [<Fact>]
 let ``optional Guid maps to Option<Guid>``() =
     let ty =
@@ -444,3 +467,35 @@ let ``PreferNullable: optional binary (base64) stays as plain Stream``() =
         compilePropertyTypeWith true "          type: string\n          format: binary\n" false
 
     ty |> shouldEqual typeof<IO.Stream>
+
+// ── PreferNullable + useDateOnly: value-type date/time formats use Nullable<T> ──────────────
+// When both provideNullable=true and useDateOnly=true, optional DateOnly/TimeOnly properties
+// should be wrapped in Nullable<T> (not Option<T>), consistent with other value types.
+
+[<Fact>]
+let ``PreferNullable: optional DateOnly maps to Nullable<DateOnly> when useDateOnly is true``() =
+    let ty =
+        compilePropertyTypeWithNullableAndDateOnly "          type: string\n          format: date\n" false
+
+    ty |> shouldEqual typeof<System.Nullable<DateOnly>>
+
+[<Fact>]
+let ``PreferNullable: required DateOnly is not wrapped when useDateOnly is true``() =
+    let ty =
+        compilePropertyTypeWithNullableAndDateOnly "          type: string\n          format: date\n" true
+
+    ty |> shouldEqual typeof<DateOnly>
+
+[<Fact>]
+let ``PreferNullable: optional TimeOnly maps to Nullable<TimeOnly> when useDateOnly is true``() =
+    let ty =
+        compilePropertyTypeWithNullableAndDateOnly "          type: string\n          format: time\n" false
+
+    ty |> shouldEqual typeof<System.Nullable<TimeOnly>>
+
+[<Fact>]
+let ``PreferNullable: required TimeOnly is not wrapped when useDateOnly is true``() =
+    let ty =
+        compilePropertyTypeWithNullableAndDateOnly "          type: string\n          format: time\n" true
+
+    ty |> shouldEqual typeof<TimeOnly>