Fix adversarial review findings: strengthen assertions and remove brittle checks

- Strengthen DueDate assertion to verify actual value (not just non-null)
- Remove trailing comma substring checks that could false-fail on string content
  (JsonDocument.Parse already validates JSON syntax)
- Replace non-deterministic if/else in cross-format test with deterministic assertion
- Rename test to match actual behavior (zero candidates, not parse error)

Author: Chris0Jeky

backend/tests/Taskdeck.Application.Tests/Services/BoardJsonExportImportRoundTripTests.cs

@@ -128,7 +128,7 @@ public async Task RoundTrip_FullBoard_PreservesAllData()
 
         var exportedCard2 = exportDto.Cards.First(c => c.Title == "Add dashboard");
         exportedCard2.Labels.Should().ContainSingle(l => l.Name == "Feature");
-        exportedCard2.DueDate.Should().NotBeNull("due date should be preserved");
+        exportedCard2.DueDate.Should().BeCloseTo(dueDate, TimeSpan.FromSeconds(1), "due date value should be preserved");
     }
 
     [Fact]
@@ -533,12 +533,8 @@ public async Task RoundTrip_ExportJsonIsValidParsableJson()
         var json = exportResult.Value;
         json.Should().NotBeNullOrWhiteSpace();
 
-        // Should not have trailing commas
-        json.Should().NotContain(",]");
-        json.Should().NotContain(",}");
-
-        // Should parse without exceptions
-        var doc = JsonDocument.Parse(json);
+        // Parsing validates JSON syntax (including rejecting trailing commas)
+        using var doc = JsonDocument.Parse(json);
         doc.Should().NotBeNull();
         doc.RootElement.ValueKind.Should().Be(JsonValueKind.Object);
     }

backend/tests/Taskdeck.Application.Tests/Services/CrossFormatImportIntegrityTests.cs

@@ -23,7 +23,7 @@ public class CrossFormatImportIntegrityTests
     };
 
     [Fact]
-    public void BoardJsonExport_FedAsCsvPayload_ProducesParseError()
+    public void BoardJsonExport_FedAsCsvPayload_ProducesZeroCandidates()
     {
         // Create a board JSON export payload
         var now = DateTimeOffset.UtcNow;
@@ -46,20 +46,11 @@ public void BoardJsonExport_FedAsCsvPayload_ProducesParseError()
 
         var result = _csvAdapter.Parse(request);
 
-        // The CSV parser should either fail or produce zero useful candidates
-        // because JSON is not valid CSV (the header row won't match expected columns)
-        if (result.IsSuccess)
-        {
-            // If it parses at all, it should not produce meaningful candidates
-            // since JSON keys don't map to expected CSV column aliases
-            result.Value.Candidates.Should().BeEmpty(
-                "JSON payload should not produce valid CSV candidates");
-        }
-        else
-        {
-            // Alternatively, the parser may reject it outright
-            result.ErrorCode.Should().NotBeNull();
-        }
+        // JSON is technically parseable as single-column CSV (the "{" line becomes the header),
+        // but no recognized column aliases exist, so zero candidates are produced.
+        result.IsSuccess.Should().BeTrue("JSON is syntactically parseable as degenerate CSV");
+        result.Value.Candidates.Should().BeEmpty(
+            "JSON payload should not produce valid CSV candidates because no column aliases match");
     }
 
     [Fact]

backend/tests/Taskdeck.Application.Tests/Services/GdprDataExportRoundTripTests.cs

@@ -120,14 +120,10 @@ public async Task ExportUserData_AllSectionsPopulated_ProducesValidJson()
         var json = JsonSerializer.Serialize(export, JsonOptions);
         json.Should().NotBeNullOrWhiteSpace();
 
-        // Parse and verify structure
-        var doc = JsonDocument.Parse(json);
+        // Parsing validates JSON syntax (including rejecting trailing commas)
+        using var doc = JsonDocument.Parse(json);
         doc.RootElement.ValueKind.Should().Be(JsonValueKind.Object);
 
-        // No trailing commas or invalid JSON
-        json.Should().NotContain(",]");
-        json.Should().NotContain(",}");
-
         // Verify the export can be deserialized back
         var deserialized = JsonSerializer.Deserialize<UserDataExportDto>(json, JsonOptions);
         deserialized.Should().NotBeNull();