git tests for sinceCommit = HEAD^^

Author: alsuren

integration_tests/__tests__/jest_changed_files.test.js

@@ -191,6 +191,19 @@ test('gets changed files for git', async () => {
       .map(filePath => path.basename(filePath))
       .sort(),
   ).toEqual(['file1.txt', 'file4.txt']);
+
+  run(`${GIT} add file4.txt`, DIR);
+  run(`${GIT} commit -m "test3"`, DIR);
+
+  ({changedFiles: files} = await getChangedFilesForRoots(roots, {
+    sinceCommit: 'HEAD^^',
+  }));
+  // Returns files from the last 2 commits
+  expect(
+    Array.from(files)
+      .map(filePath => path.basename(filePath))
+      .sort(),
+  ).toEqual(['file1.txt', 'file4.txt']);
 });
 
 test('gets changed files for hg', async () => {