Close the object for empty combination results, and keep the space in flattened messages (#1867)

Two edge cases in CombinationResultsConverter:

 * Write started an object then returned early for empty results without closing
   it, so anything written after the results was swallowed into them. Reachable
   by constructing CombinationResults directly, since the runner rejects empty
   lists.
 * FlattenMessage only appended ". " when a line did not already end in a period,
   so a line that did was run straight into the next one. The two line net48
   ArgumentNullException rendered as "Value cannot be null.Parameter name: p".

Author: SimonCropp

docs/combinations.md

@@ -198,6 +198,7 @@ public class CombinationResultsConverter :
         var items = results.Items;
         if (items.Count == 0)
         {
+            writer.WriteEndObject();
             return;
         }
 
@@ -363,16 +364,19 @@ public class CombinationResultsConverter :
             builder.Append(trimmed);
             if (!trimmed.EndsWith('.'))
             {
-                builder.Append(". ");
+                builder.Append('.');
             }
+
+            // separate from the next line even when the sentence was already terminated
+            builder.Append(' ');
         }
 
         builder.TrimEnd();
         return builder.ToString();
     }
 }
 ```
-<sup><a href='/src/Verify/Combinations/CombinationResultsConverter.cs#L1-L185' title='Snippet source file'>snippet source</a> | <a href='#snippet-CombinationResultsConverter.cs' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/Verify/Combinations/CombinationResultsConverter.cs#L1-L189' title='Snippet source file'>snippet source</a> | <a href='#snippet-CombinationResultsConverter.cs' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 

src/Verify.Tests/CombinationTests.EmptyResults.verified.txt

@@ -0,0 +1 @@
+{}

src/Verify.Tests/CombinationTests.EmptyResultsNested.verified.txt

@@ -0,0 +1,4 @@
+{
+  results: {},
+  after: TheValue
+}

src/Verify.Tests/CombinationTests.MultiLineArgumentException.verified.txt

@@ -0,0 +1,4 @@
+{
+   1: ArgumentException: Value cannot be null. Parameter name: p.,
+  10: ArgumentException: Value cannot be null. Parameter name: p.
+}

src/Verify.Tests/CombinationTests.cs

@@ -159,6 +159,38 @@ public Task RecordingWithExceptionPausedTest()
             .IgnoreStackTrace();
     }
 
+    static string ThrowMultiLine(int value) =>
+        throw new ArgumentException(
+            """
+            Value cannot be null.
+            Parameter name: p
+            """);
+
+    // ArgumentException messages are flattened onto one line, so the parts of the
+    // message need a separator between them
+    [Fact]
+    public Task MultiLineArgumentException() =>
+        Combination(captureExceptions: true)
+            .Verify(
+                ThrowMultiLine,
+                params1);
+
+    // Only reachable by constructing the results directly, since the runner requires
+    // every list to have at least one item
+    [Fact]
+    public Task EmptyResults() =>
+        Verify(new CombinationResults([], [], null));
+
+    // an unclosed object would swallow everything written after it
+    [Fact]
+    public Task EmptyResultsNested() =>
+        Verify(
+            new
+            {
+                results = new CombinationResults([], [], null),
+                after = "TheValue"
+            });
+
     [Fact]
     public Task RecordingPausedTest()
     {

src/Verify/Combinations/CombinationResultsConverter.cs

@@ -10,6 +10,7 @@ public override void Write(VerifyJsonWriter writer, CombinationResults results)
         var items = results.Items;
         if (items.Count == 0)
         {
+            writer.WriteEndObject();
             return;
         }
 
@@ -175,8 +176,11 @@ static string FlattenMessage(string message)
             builder.Append(trimmed);
             if (!trimmed.EndsWith('.'))
             {
-                builder.Append(". ");
+                builder.Append('.');
             }
+
+            // separate from the next line even when the sentence was already terminated
+            builder.Append(' ');
         }
 
         builder.TrimEnd();

src/todo.md

@@ -67,10 +67,10 @@ All six resolved 2026-08-16 (five fixed here; the inline item resolved as by-des
 - [x] **MSTest source generator ignores `record` test classes.**
   `Verify.MSTest.SourceGenerator/UsesVerifyGenerator.cs:125-126` — only `ClassDeclarationSyntax` is eligible; `[UsesVerify] [TestClass] partial record` compiles then fails at runtime with the misleading "TestContext is null" error. `Parser.GetParentClasses` similarly stops at a `record struct` parent.
 
-- [ ] **Unclosed JSON object for empty `CombinationResults`.**
+- [x] **Unclosed JSON object for empty `CombinationResults`.**
   `Verify/Combinations/CombinationResultsConverter.cs:8-14` — `WriteStartObject()` then early `return` with no `WriteEndObject()`. Only reachable by constructing `CombinationResults([], ...)` directly.
 
-- [ ] **`FlattenMessage` omits the joining space after a line ending in `.`.**
+- [x] **`FlattenMessage` omits the joining space after a line ending in `.`.**
   `Verify/Combinations/CombinationResultsConverter.cs:168-183` — two-line messages (net48 `ArgumentNullException`) render as `"Value cannot be null.Parameter name: p"`.
 
 - [ ] **Negative sub-hour offsets render unsigned.**