Use shell.exec mock

I initially try to mock the whole shelljs. But it returns error
shell.exec is not a function when i try to provide the mockResolvedValue
I think it is because of the inner code of shelljs who run a forEach to
require each of its method which make it a promise. I tried moving the
jest.mock inside beforeAll and also adding babel-dynamic-import but it did
not solve the problem. In the end, I decided to just mock shelljs.exec since
it is the only function used anyway

v1/lib/core/__tests__/utils.test.js

@@ -99,32 +99,38 @@ describe('utils', () => {
     fs.unlinkSync(tempFilePath);
 
     // test renaming and moving file
-    const tempFilePath2 = path.join(__dirname, '__fixtures__', '.temp2');
-    fs.writeFileSync(tempFilePath2, 'Lorem ipsum :)');
-
-    shell.exec(`git add ${tempFilePath2}`);
-    shell.exec(`git commit -m "Create new file" --only ${tempFilePath2}`);
-
-    const createTime = utils.getGitLastUpdated(tempFilePath2);
-    expect(typeof createTime).toBe('string');
 
-    // rename / move the file
-    fs.mkdirSync(path.join(__dirname, '__fixtures__', 'test'));
+    const tempFilePath2 = path.join(__dirname, '__fixtures__', '.temp2');
     const tempFilePath3 = path.join(
       __dirname,
       '__fixtures__',
       'test',
       '.temp3',
     );
-    shell.exec(`git mv ${tempFilePath2} ${tempFilePath3}`);
-    shell.exec(`git commit -m "Rename the file"`);
 
+    // create new file
+    shell.exec = jest.fn(() => ({
+      stdout:
+        '1539502055\n' +
+        '\n' +
+        ' create mode 100644 v1/lib/core/__tests__/__fixtures__/.temp2\n',
+    }));
+    const createTime = utils.getGitLastUpdated(tempFilePath2);
+    expect(typeof createTime).toBe('string');
+
+    // rename / move the file
+    shell.exec = jest.fn(() => ({
+      stdout:
+        '1539502056\n' +
+        '\n' +
+        ' rename v1/lib/core/__tests__/__fixtures__/{.temp2 => test/.temp3} (100%)\n' +
+        '1539502055\n' +
+        '\n' +
+        ' create mode 100644 v1/lib/core/__tests__/__fixtures__/.temp2\n',
+    }));
     const lastUpdateTime = utils.getGitLastUpdated(tempFilePath3);
+    // should only consider file content change
     expect(lastUpdateTime).toEqual(createTime);
-
-    fs.unlinkSync(tempFilePath3);
-    fs.rmdirSync(path.join(__dirname, '__fixtures__', 'test'));
-    shell.exec(`git reset HEAD^^`);
   });
 
   test('idx', () => {