test: continuous property-based fuzz via CsCheck (#81)

.github/workflows/fuzz.yaml

@@ -0,0 +1,87 @@
+# Continuous property-based fuzz.
+#
+# The Tests.Fuzz project runs in the per-PR unit sweep at CsCheck's default
+# case count — enough to catch a regression, not enough to exercise a shape a
+# consumer hits once every million rows. This workflow runs the same
+# properties at a much larger case count on a weekly cron.
+#
+# Failing cases: CsCheck auto-shrinks and prints the counter-example to test
+# output; the run's reports are uploaded as an artifact for post-mortem.
+#
+# Refs #81.
+
+name: Fuzz
+
+on:
+  workflow_dispatch:
+    inputs:
+      iterations:
+        description: "CsCheck case count per property (default 100000)"
+        required: false
+        default: "100000"
+        type: string
+  schedule:
+    # Weekly Saturday 04:00 UTC.
+    - cron: '0 4 * * 6'
+
+permissions:
+  contents: read
+
+jobs:
+  fuzz:
+    name: Continuous fuzz (${{ inputs.iterations || '100000' }} iters)
+    runs-on: ubuntu-latest
+    timeout-minutes: 60
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
+        with:
+          persist-credentials: false
+
+      # Guard so the scheduled run on main no-ops until Tests.Fuzz merges there.
+      - name: Detect Tests.Fuzz
+        id: check
+        shell: bash
+        run: |
+          if [ -f tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz.csproj ]; then
+            echo "found=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "::notice::Tests.Fuzz project not present on this ref — skipping. Merge vNext to main to enable."
+            echo "found=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Setup .NET
+        if: steps.check.outputs.found == 'true'
+        uses: actions/setup-dotnet@26b0ec14cb23fa6904739307f278c14f94c95bf1 # v5
+        with:
+          dotnet-version: 10.0.x
+
+      - name: Restore + Build Tests.Fuzz (Release)
+        if: steps.check.outputs.found == 'true'
+        run: |
+          dotnet restore tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz.csproj
+          dotnet build tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz.csproj \
+            --no-restore --configuration Release
+
+      - name: Run fuzz suite
+        if: steps.check.outputs.found == 'true'
+        env:
+          CsCheck_Iterations: ${{ inputs.iterations || '100000' }}
+          CsCheck_Timeout: "1800000"    # 30 min per property
+        run: |
+          mkdir -p reports
+          dotnet test tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz.csproj \
+            --no-build --configuration Release \
+            --filter 'Category=Fuzz' \
+            --logger "console;verbosity=detailed" \
+            --logger "trx;LogFileName=fuzz.trx" \
+            --results-directory reports/ \
+            2>&1 | tee reports/fuzz.log
+
+      - name: Upload fuzz reports
+        if: always()
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7
+        with:
+          name: fuzz-reports
+          path: reports/
+          retention-days: 60

ETL-SqlBulkCopy.slnx

@@ -57,5 +57,6 @@
     <Project Path="tests/Wolfgang.Etl.SqlBulkCopy.Tests.Integration/Wolfgang.Etl.SqlBulkCopy.Tests.Integration.csproj" />
     <Project Path="tests/Wolfgang.Etl.SqlBulkCopy.Tests.DocExamples/Wolfgang.Etl.SqlBulkCopy.Tests.DocExamples.csproj" />
     <Project Path="tests/Wolfgang.Etl.SqlBulkCopy.AotSmoke/Wolfgang.Etl.SqlBulkCopy.AotSmoke.csproj" />
+    <Project Path="tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz.csproj" />
   </Folder>
 </Solution>

src/Wolfgang.Etl.SqlBulkCopy/Properties/AssemblyInfo.cs

@@ -4,3 +4,4 @@
 [assembly: InternalsVisibleTo("Wolfgang.Etl.SqlBulkCopy.Tests.Integration")]
 [assembly: InternalsVisibleTo("Wolfgang.Etl.SqlBulkCopy.Benchmarks")]
 [assembly: InternalsVisibleTo("Wolfgang.Etl.SqlBulkCopy.AotSmoke")]
+[assembly: InternalsVisibleTo("Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz")]

tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/FuzzRecord.cs

@@ -0,0 +1,18 @@
+namespace Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz;
+
+/// <summary>
+/// A mappable record shape with a spread of column kinds (value type, reference
+/// type, nullable value type, bool) used by the fuzz properties. Field values
+/// are generated by CsCheck; the type itself is fixed because CsCheck cannot
+/// generate .NET types dynamically.
+/// </summary>
+public sealed class FuzzRecord
+{
+    public int A { get; set; }
+
+    public string B { get; set; } = string.Empty;
+
+    public int? C { get; set; }
+
+    public bool D { get; set; }
+}

tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/MappingFuzz.cs

@@ -0,0 +1,120 @@
+// Continuous property-based fuzz over the type-mapping layer.
+//
+// The per-PR unit + conformance suites cover hand-picked shapes; this asks
+// CsCheck to generate large numbers of parameterised inputs ([Trait
+// "Category=Fuzz"]) and asserts per-input invariants that must hold across
+// every generated value. Case count comes from CsCheck_Iterations (set by
+// fuzz.yaml for the scheduled run; small by default for local iteration).
+// A failing input auto-shrinks to a minimal counter-example.
+//
+// Refs #81.
+
+using System.Text;
+using CsCheck;
+using Wolfgang.Etl.SqlBulkCopy;
+using Xunit;
+
+namespace Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz;
+
+public class MappingFuzz
+{
+    /// <summary>
+    /// For any non-blank schema/table override, the bracket-quoting applied by
+    /// <c>QualifiedTableName</c> must round-trip: un-quoting the result (undoubling
+    /// <c>]]</c>) recovers the exact original identifiers. Catches any escaping
+    /// bug that would let an identifier break out of its brackets.
+    /// </summary>
+    [Fact]
+    [Trait("Category", "Fuzz")]
+    public void QualifiedTableName_bracket_quoting_round_trips()
+    {
+        Gen.Select(Gen.String, Gen.String).Sample((schema, table) =>
+        {
+            // Blank overrides normalise to the type's attribute default rather
+            // than the override, so they aren't part of this invariant.
+            if (string.IsNullOrWhiteSpace(schema) || string.IsNullOrWhiteSpace(table))
+            {
+                return true;
+            }
+
+            var map = TypeMap.Create(typeof(FuzzRecord), schema, table);
+            var (recoveredSchema, recoveredTable) = Unbracket(map.QualifiedTableName);
+
+            return string.Equals(recoveredSchema, schema, System.StringComparison.Ordinal)
+                   && string.Equals(recoveredTable, table, System.StringComparison.Ordinal);
+        });
+    }
+
+
+
+    /// <summary>
+    /// For any record value, every mapped column's getter must return exactly
+    /// what reflection reads from the same property. This exercises the compiled
+    /// (or source-generated) getter path across arbitrary values.
+    /// </summary>
+    [Fact]
+    [Trait("Category", "Fuzz")]
+    public void ColumnMap_GetValue_matches_the_property_value()
+    {
+        var nullableInt = Gen.Int.Select(x => x % 7 == 0 ? (int?)null : x);
+
+        Gen.Select(Gen.Int, Gen.String, nullableInt, Gen.Bool).Sample((a, b, c, d) =>
+        {
+            var instance = new FuzzRecord { A = a, B = b ?? string.Empty, C = c, D = d };
+            var map = TypeMap.Create(typeof(FuzzRecord));
+
+            foreach (var column in map.Columns)
+            {
+                var property = typeof(FuzzRecord).GetProperty(column.PropertyName)!;
+                if (!Equals(property.GetValue(instance), column.GetValue(instance)))
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        });
+    }
+
+
+
+    // Inverse of TypeMap's `[schema].[table]` quoting, where a literal ']' inside
+    // an identifier is doubled to ']]'.
+    private static (string Schema, string Table) Unbracket(string qualified)
+    {
+        var index = 0;
+        var schema = ReadBracketedSegment(qualified, ref index);
+        index++; // skip the '.' separator between the two segments
+        var table = ReadBracketedSegment(qualified, ref index);
+        return (schema, table);
+    }
+
+
+
+    private static string ReadBracketedSegment(string value, ref int index)
+    {
+        index++; // skip the opening '['
+        var builder = new StringBuilder();
+
+        while (index < value.Length)
+        {
+            if (value[index] == ']')
+            {
+                if (index + 1 < value.Length && value[index + 1] == ']')
+                {
+                    builder.Append(']');
+                    index += 2;
+                    continue;
+                }
+
+                index++; // consume the closing ']'
+                break;
+            }
+
+            builder.Append(value[index]);
+            index++;
+        }
+
+        return builder.ToString();
+    }
+}

tests/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz/Wolfgang.Etl.SqlBulkCopy.Tests.Fuzz.csproj

@@ -0,0 +1,34 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <!-- net10.0 only: CsCheck is generator-driven; running the same property
+         across every TFM adds hours to a scheduled fuzz run without materially
+         widening coverage. TFM-conditional behaviour is caught by pr.yaml's
+         per-TFM unit sweep. -->
+    <TargetFramework>net10.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+
+    <!-- Fuzz-property assemblies are permitted broader shapes than library code. -->
+    <NoWarn>$(NoWarn);MA0004;S1144;S6966;NU1903;CA1707;CA1062;CA2007</NoWarn>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Wolfgang.Etl.SqlBulkCopy\Wolfgang.Etl.SqlBulkCopy.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" allowedVersions="(,3.0.0)">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="CsCheck" Version="4.0.0" />
+    <PackageReference Include="JetBrains.Annotations" Version="2024.3.0" PrivateAssets="all" />
+  </ItemGroup>
+
+</Project>