Add test_it_falls_back_to_direct_diff_if_merge_base_is_not_availabe

tests/phpunit/Logger/GitHub/GitDiffFileProviderTest.php

@@ -38,6 +38,7 @@
 use Infection\Logger\GitHub\GitDiffFileProvider;
 use Infection\Logger\GitHub\NoFilesInDiffToMutate;
 use Infection\Process\ShellCommandLineExecutor;
+use Symfony\Component\Process\Exception\ProcessFailedException;
 use const PHP_OS_FAMILY;
 use PHPUnit\Framework\TestCase;
 
@@ -87,6 +88,31 @@ public function test_it_executes_diff_and_returns_filter_as_a_string(): void
         $this->assertSame('src/A.php,src/B.php', $filter);
     }
 
+    public function test_it_falls_back_to_direct_diff_if_merge_base_is_not_availabe(): void
+    {
+        $expectedMergeBaseCommandLine = 'git merge-base \'master\' HEAD';
+        $shellCommandLineExecutor = $this->createMock(ShellCommandLineExecutor::class);
+        $expectedDiffCommandLine = 'git diff \'master\' --diff-filter=\'AM\' --name-only | grep src/ | paste -s -d "," -';
+
+        $shellCommandLineExecutor->expects($this->any())
+            ->method('execute')
+            ->willReturnCallback(function (string $command) use ($expectedDiffCommandLine, $expectedMergeBaseCommandLine): string {
+                switch ($command) {
+                    case $expectedMergeBaseCommandLine:
+                        throw $this->createStub(ProcessFailedException::class);
+                    case $expectedDiffCommandLine:
+                        return 'src/A.php,src/B.php';
+                    default:
+                        $this->fail("Unexpected shell command: $command");
+                }
+            });
+
+        $diffProvider = new GitDiffFileProvider($shellCommandLineExecutor);
+        $filter = $diffProvider->provide('AM', 'master');
+
+        $this->assertSame('src/A.php,src/B.php', $filter);
+    }
+
     public function test_it_provides_lines_filter_as_a_string(): void
     {
         $expectedMergeBaseCommandLine = 'git merge-base \'master\' HEAD';