Prevent drifting inline snapshots #8424 (#8492)

* Prevent drifting inline snapshots #8424

Fixes #8424 by avoiding indenting inline snapshot if second
line of inline snapshot already has been indented.

* Added pull request to changelog

* Fixed review comment

Also added a short comment to the code describing its purpose.

CHANGELOG.md

@@ -10,6 +10,7 @@
 
 - `[babel-plugin-jest-hoist]` Expand list of whitelisted globals in global mocks ([#8429](https://github.com/facebook/jest/pull/8429)
 - `[jest-core]` Make watch plugin initialization errors look nice ([#8422](https://github.com/facebook/jest/pull/8422))
+- `[jest-snapshot]` Prevent inline snapshots from drifting when inline snapshots are updated ([#8492](https://github.com/facebook/jest/pull/8492))
 
 ### Chore & Maintenance
 

packages/jest-snapshot/src/__tests__/inline_snapshots.test.ts

@@ -236,6 +236,56 @@ test('saveInlineSnapshots() indents multi-line snapshots with spaces', () => {
   );
 });
 
+test('saveInlineSnapshots() does not re-indent already indented snapshots', () => {
+  const filename = path.join(__dirname, 'my.test.js');
+  (fs.readFileSync as jest.Mock).mockImplementation(
+    () =>
+      "it('is a test', () => {\n" +
+      "  expect({a: 'a'}).toMatchInlineSnapshot();\n" +
+      '});\n' +
+      "it('is a another test', () => {\n" +
+      "  expect({a: 'a'}).toMatchInlineSnapshot(`\n" +
+      '    Object {\n' +
+      "      b: 'b'\n" +
+      '    }\n' +
+      '  `);\n' +
+      '});\n',
+  );
+  (prettier.resolveConfig.sync as jest.Mock).mockReturnValue({
+    bracketSpacing: false,
+    singleQuote: true,
+  });
+
+  saveInlineSnapshots(
+    [
+      {
+        frame: {column: 20, file: filename, line: 2} as Frame,
+        snapshot: `\nObject {\n  a: 'a'\n}\n`,
+      },
+    ],
+    prettier,
+    babelTraverse,
+  );
+
+  expect(fs.writeFileSync).toHaveBeenCalledWith(
+    filename,
+    "it('is a test', () => {\n" +
+      "  expect({a: 'a'}).toMatchInlineSnapshot(`\n" +
+      '    Object {\n' +
+      "      a: 'a'\n" +
+      '    }\n' +
+      '  `);\n' +
+      '});\n' +
+      "it('is a another test', () => {\n" +
+      "  expect({a: 'a'}).toMatchInlineSnapshot(`\n" +
+      '    Object {\n' +
+      "      b: 'b'\n" +
+      '    }\n' +
+      '  `);\n' +
+      '});\n',
+  );
+});
+
 test('saveInlineSnapshots() indents multi-line snapshots with tabs', () => {
   const filename = path.join(__dirname, 'my.test.js');
   (fs.readFileSync as jest.Mock).mockImplementation(

packages/jest-snapshot/src/inline_snapshots.ts

@@ -120,6 +120,14 @@ const groupSnapshotsByFile = groupSnapshotsBy(({frame: {file}}) => file);
 
 const indent = (snapshot: string, numIndents: number, indentation: string) => {
   const lines = snapshot.split('\n');
+  // Prevent re-identation of inline snapshots.
+  if (
+    lines.length >= 2 &&
+    lines[1].startsWith(indentation.repeat(numIndents + 1))
+  ) {
+    return snapshot;
+  }
+
   return lines
     .map((line, index) => {
       if (index === 0) {