fix: coverage merger

src/Plugins/Tia/CoverageMerger.php

@@ -8,6 +8,9 @@ use Pest\Plugins\Tia;
 use Pest\Plugins\Tia\Contracts\State;
 use Pest\Support\Container;
 use SebastianBergmann\CodeCoverage\CodeCoverage;
+use SebastianBergmann\CodeCoverage\Driver\Selector;
+use SebastianBergmann\CodeCoverage\Filter;
+use SebastianBergmann\CodeCoverage\Serialization\Unserializer;
 use Throwable;
 
 /**
@@ -161,7 +164,60 @@ final class CoverageMerger
             return null;
         }
 
-        return $value instanceof CodeCoverage ? $value : null;
+        // Legacy `--coverage-php` format: a serialized `CodeCoverage` object.
+        if ($value instanceof CodeCoverage) {
+            return $value;
+        }
+
+        // Since phpunit/php-code-coverage 14, `--coverage-php` writes the report
+        // as a serialized array (`['codeCoverage' => ..., 'testResults' => ...,
+        // 'basePath' => ...]`) rather than a `CodeCoverage` object, so it has to
+        // be rebuilt into one before it can be merged.
+        return self::coverageFromSerializedData($reportPath);
+    }
+
+    private static function coverageFromSerializedData(string $reportPath): ?CodeCoverage
+    {
+        if ($reportPath === '') {
+            return null;
+        }
+
+        try {
+            $serialized = new Unserializer()->unserialize($reportPath);
+        } catch (Throwable) {
+            return null;
+        }
+
+        $data = $serialized['codeCoverage'];
+        $basePath = $serialized['basePath'];
+
+        if ($basePath !== '') {
+            foreach ($data->coveredFiles() as $relativePath) {
+                $data->renameFile($relativePath, $basePath.DIRECTORY_SEPARATOR.$relativePath);
+            }
+        }
+
+        $coverage = self::emptyCoverage();
+
+        if (! $coverage instanceof CodeCoverage) {
+            return null;
+        }
+
+        $coverage->setData($data);
+        $coverage->setTests($serialized['testResults']);
+
+        return $coverage;
+    }
+
+    private static function emptyCoverage(): ?CodeCoverage
+    {
+        try {
+            $filter = new Filter;
+
+            return new CodeCoverage(new Selector()->forLineCoverage($filter), $filter);
+        } catch (Throwable) {
+            return null;
+        }
     }
 
     private static function unserializeCoverage(string $bytes): ?CodeCoverage