Add Infection and configure mutation testing in CI

Author: ciaranmcnulty

.github/workflows/test-php.yml

@@ -53,6 +53,17 @@ jobs:
           vendor/bin/psalm --no-cache
           vendor/bin/phpunit --testsuite unit
 
-      - name: run acceptance tests
+      - name: Run acceptance tests
         run: make acceptance
         working-directory: php
+
+      - name: Mutation tests - minimum thresholds
+        run: |
+          vendor/bin/infection --min-msi=85 --min-covered-msi=88
+        working-directory: php
+
+      - name: Mutation tests - modifications
+        run: |
+          git fetch --depth=1 origin $GITHUB_BASE_REF
+          vendor/bin/infection --git-diff-lines --git-diff-base=origin/$GITHUB_BASE_REF --logger-github --ignore-msi-with-no-mutations
+        working-directory: php

php/composer.json

@@ -22,7 +22,8 @@
         "vimeo/psalm": "^4.24",
         "friendsofphp/php-cs-fixer": "^3.5",
         "psalm/plugin-phpunit": "^0.18.0",
-        "nikic/php-parser": "^4.14"
+        "nikic/php-parser": "^4.14",
+        "infection/infection": "^0.26.16"
     },
     "repositories": [
         {
@@ -34,5 +35,10 @@
                 }
             }
         }
-    ]
+    ],
+    "config": {
+        "allow-plugins": {
+            "infection/extension-installer": false
+        }
+    }
 }

php/infection.json5

@@ -0,0 +1,11 @@
+{
+    "$schema": "vendor/infection/infection/resources/schema.json",
+    "source": {
+        "directories": [
+            "src",
+        ]
+    },
+    "mutators": {
+        "@default": true
+    }
+}