Feature: Add runtimeHooksPath options with onBeforeWriteToDiscPath in it

README.md

@@ -123,6 +123,9 @@ See [the examples](./examples/README.md) for more detailed usage or read about a
 * `dumpDiffToConsole`: (default `false`) Will output base64 string of a diff image to console in case of failed tests (in addition to creating a diff image). This string can be copy-pasted to a browser address string to preview the diff for a failed test.
 * `dumpInlineDiffToConsole`: (default `false`) Will output the image to the terminal using iTerm's [Inline Images Protocol](https://iterm2.com/documentation-images.html). If the term is not compatible, it does the same thing as `dumpDiffToConsole`.
 * `allowSizeMismatch`: (default `false`) If set to true, the build will not fail when the screenshots to compare have different sizes.
+* `runtimeHooksPath`: (default `undefined`) This needs to be set to a existing file, like `require.resolve('./runtimeHooksPath.cjs')`. This file can expose a few hooks:
+  * `onBeforeWriteToDisc`: before saving any image to the disc, this function will be called (can be used to write EXIF data to images for instance)
+    `onBeforeWriteToDisc: (arguments: { buffer: Buffer; destination: string; testPath: string; currentTestName: string }) => Buffer`
 
 ```javascript
 it('should demonstrate this matcher`s usage with a custom pixelmatch config', () => {

__tests__/__snapshots__/index.spec.js.snap

@@ -42,6 +42,7 @@ exports[`toMatchImageSnapshot passes diffImageToSnapshot everything it needs to
   "allowSizeMismatch": false,
   "blur": 0,
   "comparisonMethod": "pixelmatch",
+  "currentTestName": "test",
   "customDiffConfig": {},
   "diffDir": undefined,
   "diffDirection": "horizontal",
@@ -50,9 +51,11 @@ exports[`toMatchImageSnapshot passes diffImageToSnapshot everything it needs to
   "onlyDiff": false,
   "receivedDir": undefined,
   "receivedImageBuffer": "pretendthisisanimagebuffer",
+  "runtimeHooksPath": undefined,
   "snapshotIdentifier": "test-spec-js-test-1-snap",
   "snapshotsDir": "path/to/__image_snapshots__",
   "storeReceivedOnFailure": false,
+  "testPath": "path/to/test.spec.js",
   "updatePassedSnapshot": false,
   "updateSnapshot": false,
 }

__tests__/diff-snapshot.spec.js

@@ -826,6 +826,73 @@ describe('diff-snapshot', () => {
 
       expect(mockMkdirSync).toHaveBeenCalledWith(path.join(mockSnapshotsDir, '__diff_output__'), { recursive: true });
     });
+
+    it('should pass data to a file mentioned by runtimeHooksPath when writing files', () => {
+      jest.doMock(require.resolve('./stubs/runtimeHooksPath.js'), () => ({
+        onBeforeWriteToDisc: jest.fn(({ buffer }) => buffer),
+      }));
+      const { onBeforeWriteToDisc } = require('./stubs/runtimeHooksPath');
+
+      const diffImageToSnapshot = setupTest({ snapshotExists: false, pixelmatchResult: 0 });
+      const result = diffImageToSnapshot({
+        receivedImageBuffer: mockImageBuffer,
+        snapshotIdentifier: mockSnapshotIdentifier,
+        snapshotsDir: mockSnapshotsDir,
+        receivedDir: mockReceivedDir,
+        diffDir: mockDiffDir,
+        failureThreshold: 0,
+        failureThresholdType: 'pixel',
+        runtimeHooksPath: require.resolve('./stubs/runtimeHooksPath.js'),
+        testPath: 'test.spec.js',
+        currentTestName: 'test a',
+      });
+
+      expect(result).toMatchObject({
+        added: true,
+      });
+
+      expect(onBeforeWriteToDisc).toHaveBeenCalledTimes(1);
+      expect(onBeforeWriteToDisc).toHaveBeenCalledWith({
+        buffer: mockImageBuffer,
+        destination: '/path/to/snapshots/id1.png',
+        testPath: 'test.spec.js',
+        currentTestName: 'test a',
+      });
+    });
+
+    it('should work even when runtimeHooksPath is invalid', () => {
+      const diffImageToSnapshot = setupTest({ snapshotExists: false, pixelmatchResult: 0 });
+      expect(() => diffImageToSnapshot({
+        receivedImageBuffer: mockImageBuffer,
+        snapshotIdentifier: mockSnapshotIdentifier,
+        snapshotsDir: mockSnapshotsDir,
+        receivedDir: mockReceivedDir,
+        diffDir: mockDiffDir,
+        failureThreshold: 0,
+        failureThresholdType: 'pixel',
+        runtimeHooksPath: './non-existing-file.js',
+      })).toThrowError(
+        new Error("Couldn't import ./non-existing-file.js: Cannot find module './non-existing-file.js' from 'src/diff-snapshot.js'")
+      );
+
+      jest.doMock(require.resolve('./stubs/runtimeHooksPath.js'), () => ({
+        onBeforeWriteToDisc: () => {
+          throw new Error('wrong');
+        },
+      }));
+      expect(() => diffImageToSnapshot({
+        receivedImageBuffer: mockImageBuffer,
+        snapshotIdentifier: mockSnapshotIdentifier,
+        snapshotsDir: mockSnapshotsDir,
+        receivedDir: mockReceivedDir,
+        diffDir: mockDiffDir,
+        failureThreshold: 0,
+        failureThresholdType: 'pixel',
+        runtimeHooksPath: require.resolve('./stubs/runtimeHooksPath.js'),
+      })).toThrowError(
+        new Error("Couldn't execute onBeforeWriteToDisc: wrong")
+      );
+    });
   });
 });
 

__tests__/index.spec.js

@@ -441,15 +441,20 @@ describe('toMatchImageSnapshot', () => {
       allowSizeMismatch: false,
       blur: 0,
       comparisonMethod: 'pixelmatch',
+      currentTestName: 'test1',
       customDiffConfig: {},
+      diffDir: undefined,
       diffDirection: 'horizontal',
       onlyDiff: false,
       failureThreshold: 0,
       failureThresholdType: 'pixel',
+      receivedDir: undefined,
       receivedImageBuffer: undefined,
+      runtimeHooksPath: undefined,
       snapshotIdentifier: 'test-spec-js-test-1-1-snap',
       snapshotsDir: 'path/to/__image_snapshots__',
       storeReceivedOnFailure: false,
+      testPath: 'path/to/test.spec.js',
       updatePassedSnapshot: false,
       updateSnapshot: false,
     });
@@ -508,13 +513,17 @@ describe('toMatchImageSnapshot', () => {
       customDiffConfig: {
         perceptual: true,
       },
+      currentTestName: 'test1',
       snapshotIdentifier: 'custom-test-spec-js-test-1-1',
       snapshotsDir: path.join('path', 'to', 'my-custom-snapshots-dir'),
       receivedDir: path.join('path', 'to', 'my-custom-received-dir'),
+      receivedImageBuffer: undefined,
+      runtimeHooksPath: undefined,
       storeReceivedOnFailure: true,
       diffDir: path.join('path', 'to', 'my-custom-diff-dir'),
       diffDirection: 'vertical',
       onlyDiff: false,
+      testPath: 'path/to/test.spec.js',
       updateSnapshot: false,
       updatePassedSnapshot: true,
       failureThreshold: 1,
@@ -571,16 +580,20 @@ describe('toMatchImageSnapshot', () => {
       },
       snapshotIdentifier: 'test-spec-js-test-1-1-snap',
       snapshotsDir: path.join('path', 'to', 'my-custom-snapshots-dir'),
+      receivedImageBuffer: undefined,
+      runtimeHooksPath: undefined,
       receivedDir: path.join('path', 'to', 'my-custom-received-dir'),
       diffDir: path.join('path', 'to', 'my-custom-diff-dir'),
       diffDirection: 'horizontal',
       onlyDiff: false,
       storeReceivedOnFailure: true,
+      testPath: 'path/to/test.spec.js',
       updateSnapshot: false,
       updatePassedSnapshot: false,
       failureThreshold: 0,
       failureThresholdType: 'pixel',
       comparisonMethod: 'pixelmatch',
+      currentTestName: 'test1',
     });
     expect(Chalk).toHaveBeenCalledWith({
       level: 0, // noColors

__tests__/stubs/runtimeHooksPath.js

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2017 American Express Travel Related Services Company, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+exports.onBeforeWriteToDisc = buffer => buffer;

package.json

@@ -30,7 +30,7 @@
       "!test-results/**"
     ],
     "testMatch": [
-      "<rootDir>/__tests__/**/*.js"
+      "<rootDir>/__tests__/**/*.spec.js"
     ],
     "coveragePathIgnorePatterns": [
       "/node_modules/",

src/diff-snapshot.js

@@ -219,14 +219,43 @@ function diffImageToSnapshot(options) {
     blur,
     allowSizeMismatch = false,
     comparisonMethod = 'pixelmatch',
+    testPath,
+    currentTestName,
+    runtimeHooksPath,
   } = options;
 
+  const writeFileSync = (pathToFile, content) => {
+    let finalContent = content;
+    if (runtimeHooksPath) {
+      let runtimeHooks;
+      try {
+        // As `diffImageToSnapshot` can be called in a worker, and as we cannot pass a function
+        // to a worker, we need to use an external file path that can be imported
+        // eslint-disable-next-line import/no-dynamic-require, global-require
+        runtimeHooks = require(runtimeHooksPath);
+      } catch (e) {
+        throw new Error(`Couldn't import ${runtimeHooksPath}: ${e.message}`);
+      }
+      try {
+        finalContent = runtimeHooks.onBeforeWriteToDisc({
+          buffer: content,
+          destination: pathToFile,
+          testPath,
+          currentTestName,
+        });
+      } catch (e) {
+        throw new Error(`Couldn't execute onBeforeWriteToDisc: ${e.message}`);
+      }
+    }
+    fs.writeFileSync(pathToFile, finalContent);
+  };
+
   const comparisonFn = comparisonMethod === 'ssim' ? ssimMatch : pixelmatch;
   let result = {};
   const baselineSnapshotPath = path.join(snapshotsDir, `${snapshotIdentifier}.png`);
   if (!fs.existsSync(baselineSnapshotPath)) {
     fs.mkdirSync(path.dirname(baselineSnapshotPath), { recursive: true });
-    fs.writeFileSync(baselineSnapshotPath, receivedImageBuffer);
+    writeFileSync(baselineSnapshotPath, receivedImageBuffer);
     result = { added: true };
   } else {
     const receivedSnapshotPath = path.join(receivedDir, `${snapshotIdentifier}-received.png`);
@@ -294,7 +323,7 @@ function diffImageToSnapshot(options) {
     if (isFailure({ pass, updateSnapshot })) {
       if (storeReceivedOnFailure) {
         fs.mkdirSync(path.dirname(receivedSnapshotPath), { recursive: true });
-        fs.writeFileSync(receivedSnapshotPath, receivedImageBuffer);
+        writeFileSync(receivedSnapshotPath, receivedImageBuffer);
         result = { receivedSnapshotPath };
       }
 
@@ -320,7 +349,7 @@ function diffImageToSnapshot(options) {
       // Set filter type to Paeth to avoid expensive auto scanline filter detection
       // For more information see https://www.w3.org/TR/PNG-Filters.html
       const pngBuffer = PNG.sync.write(compositeResultImage, { filterType: 4 });
-      fs.writeFileSync(diffOutputPath, pngBuffer);
+      writeFileSync(diffOutputPath, pngBuffer);
 
       result = {
         ...result,
@@ -334,7 +363,7 @@ function diffImageToSnapshot(options) {
       };
     } else if (shouldUpdate({ pass, updateSnapshot, updatePassedSnapshot })) {
       fs.mkdirSync(path.dirname(baselineSnapshotPath), { recursive: true });
-      fs.writeFileSync(baselineSnapshotPath, receivedImageBuffer);
+      writeFileSync(baselineSnapshotPath, receivedImageBuffer);
       result = { updated: true };
     } else {
       result = {

src/index.js

@@ -139,6 +139,7 @@ function configureToMatchImageSnapshot({
   customReceivedDir: commonCustomReceivedDir,
   customDiffDir: commonCustomDiffDir,
   onlyDiff: commonOnlyDiff = false,
+  runtimeHooksPath: commonRuntimeHooksPath = undefined,
   diffDirection: commonDiffDirection = 'horizontal',
   noColors: commonNoColors,
   failureThreshold: commonFailureThreshold = 0,
@@ -158,6 +159,7 @@ function configureToMatchImageSnapshot({
     customReceivedDir = commonCustomReceivedDir,
     customDiffDir = commonCustomDiffDir,
     onlyDiff = commonOnlyDiff,
+    runtimeHooksPath = commonRuntimeHooksPath,
     diffDirection = commonDiffDirection,
     customDiffConfig = {},
     noColors = commonNoColors,
@@ -220,6 +222,8 @@ function configureToMatchImageSnapshot({
         receivedDir,
         diffDir,
         diffDirection,
+        testPath,
+        currentTestName,
         onlyDiff,
         snapshotIdentifier,
         updateSnapshot: snapshotState._updateSnapshot === 'all',
@@ -230,6 +234,7 @@ function configureToMatchImageSnapshot({
         blur,
         allowSizeMismatch,
         comparisonMethod,
+        runtimeHooksPath,
       });
 
     return checkResult({