Add mutation testing to feature branches

Closes #502

.github/workflows/branch-feature.yml

@@ -33,4 +33,11 @@ jobs:
   check-markdown:
     needs: [get-version]
     uses: ./.github/workflows/step-check-markdown.yml
-    secrets: inherit
+    secrets: inherit
+
+  mutation-testing:
+    needs: [get-version]
+    uses: ./.github/workflows/step-mutation-testing.yml
+    secrets: inherit
+    with:
+      comparison: ${{ github.base_ref }}

.github/workflows/step-mutation-testing.yml

@@ -0,0 +1,26 @@
+on:
+  workflow_call:
+    inputs:
+      comparison:
+        type: string
+        description: 'The comparison to use for the mutation testing'
+        required: true
+env:
+  MAJOR_DOTNET_VERSION: 8
+
+jobs:
+  mutation-testing:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+      - name: Setup .NET Core
+        uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: ${{ env.MAJOR_DOTNET_VERSION }}.0.x
+      - name: Install Stryker
+        run: |
+          dotnet tool install -g dotnet-stryker
+      - name: Run Stryker
+        run: |
+          dotnet stryker --since:${{ inputs.comparison }}

stryker-config.json

@@ -0,0 +1,32 @@
+{
+  "stryker-config":
+  {
+    "solution": "Html2Markdown.sln",
+    "project": "Html2Markdown.csproj",
+    "thresholds": {
+      "high": 95,
+      "low": 85,
+      "break": 80
+    },
+    "since": {
+      "target": "develop",
+      "ignore-changes-in": [
+        "**.md",
+        "/.cm/**",
+        "/.github/**",
+        "/.git/**",
+        "/.idea/**",
+        "/.StrykerOutput/**",
+        ".gitignore",
+        ".gitmessage",
+        "build.cake",
+        "markdownlint.json",
+        "doxygen.config",
+        "*.DotSettings",
+        "*.DotSettings.user",
+        "License.txt",
+        "semver.json"
+      ]
+    }
+  }
+}