Add a failing test for printSnapshotAndReceived incorrectly recognizing sometimes indented lines as changed

packages/jest-snapshot/src/__tests__/__snapshots__/printSnapshot.test.ts.snap

@@ -375,6 +375,24 @@ Snapshot: <m>"delete"</>
 Received: <t>"insert"</>
 `;
 
+exports[`printSnapshotAndReceived ignore indentation ignores custom indentation of unchanged line 1`] = `
+<m>- Snapshot  - 2</>
+<t>+ Received  + 2</>
+
+<m>-   **some plugin-generated string with custom leading whitespace**</>
+<t>+   **some plugin-generated string with custom leading whitespace**</>
+
+<d>  Object {</>
+<d>    "props": Object {</>
+<d>      "alt": "Jest logo",</>
+<m>-     "class": "logo",</>
+<t>+     "class": "logo round",</>
+<d>      "src": "/img/jest.svg",</>
+<d>    },</>
+<d>    "type": "img",</>
+<d>  }</>
+`;
+
 exports[`printSnapshotAndReceived ignore indentation markup delete 1`] = `
 <m>- Snapshot  - 2</>
 <t>+ Received  + 0</>

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

@@ -8,7 +8,7 @@
 import ansiRegex = require('ansi-regex');
 import styles = require('ansi-styles');
 import chalk = require('chalk');
-import format from 'pretty-format';
+import format, {NewPlugin} from 'pretty-format';
 import {
   aBackground2,
   aBackground3,
@@ -20,6 +20,7 @@ import {
   bForeground3,
 } from '../colors';
 import {
+  addSerializer,
   toMatchInlineSnapshot,
   toMatchSnapshot,
   toThrowErrorMatchingInlineSnapshot,
@@ -137,6 +138,19 @@ expect.addSnapshotSerializer({
   },
 });
 
+let customSerializer: NewPlugin | null = null;
+addSerializer({
+  serialize(...args) {
+    return customSerializer!.serialize(...args);
+  },
+  test(val) {
+    if (!customSerializer) {
+      return false;
+    }
+    return customSerializer.test(val);
+  },
+});
+
 describe('chalk', () => {
   // Because these tests give code coverage of get functions
   // and give confidence that the escape sequences are correct,
@@ -1267,6 +1281,52 @@ describe('printSnapshotAndReceived', () => {
       expect(testWithStringify(expected, received, false)).toMatchSnapshot();
     });
 
+    test('ignores custom indentation of unchanged line', () => {
+      try {
+        const pluginGeneratedContent =
+          '  **some plugin-generated string with custom leading whitespace**\n\n';
+        const seen = new WeakSet();
+
+        const plugin: NewPlugin = {
+          serialize: (val, config, indentation, depth, refs, printer) => {
+            seen.add(val);
+            const serialized = printer(val, config, indentation, depth, refs);
+            seen.delete(val);
+            return pluginGeneratedContent + serialized;
+          },
+          test: val => typeof val === 'object' && val.props && !seen.has(val),
+        };
+
+        customSerializer = plugin;
+
+        const snapshot = {
+          props: {
+            alt: 'Jest logo',
+            class: 'logo',
+            src: '/img/jest.svg',
+          },
+          type: 'img',
+        };
+        const received = {
+          ...snapshot,
+          props: {
+            ...snapshot.props,
+            class: 'logo round',
+          },
+        };
+        expect(
+          printSnapshotAndReceived(
+            serialize(snapshot),
+            serialize(received),
+            received,
+            true,
+          ),
+        ).toMatchSnapshot();
+      } finally {
+        customSerializer = null;
+      }
+    });
+
     describe('object', () => {
       const text = 'Ignore indentation in snapshot';
       const time = '2019-11-11';