perf(diff-snapshot): remove logic to bypass diff for identical images

pixelmatch now handles this for us

Author: anescobar1991

__tests__/diff-snapshot.spec.js

@@ -138,8 +138,6 @@ describe('diff-snapshot', () => {
         diffPixelCount: 0,
         pass: true,
       });
-      // Check that pixelmatch was not called
-      expect(mockPixelMatch).not.toHaveBeenCalled();
     });
 
     it('it should not write a diff if a test passes', () => {
@@ -160,8 +158,6 @@ describe('diff-snapshot', () => {
         diffPixelCount: 0,
         pass: true,
       });
-      // Check that pixelmatch was not called
-      expect(mockPixelMatch).not.toHaveBeenCalled();
 
       // Check that that it did not attempt to write a diff
       expect(mockWriteFileSync.mock.calls).toEqual([]);
@@ -348,7 +344,14 @@ describe('diff-snapshot', () => {
       });
 
       // Check that pixelmatch was not called
-      expect(mockPixelMatch).not.toHaveBeenCalled();
+      expect(mockPixelMatch).toHaveBeenCalledWith(
+        expect.any(Object), // buffer data
+        expect.any(Object), // buffer data
+        expect.any(Object), // buffer data
+        expect.any(Number), // image width
+        expect.any(Number), // image height
+        { threshold: 0.01 }
+      );
     });
 
     it('should merge custom configuration with default configuration if custom config is passed', () => {
@@ -361,15 +364,21 @@ describe('diff-snapshot', () => {
         diffDir: mockDiffDir,
         updateSnapshot: false,
         customDiffConfig: {
-          threshold: 0.1,
           foo: 'bar',
         },
         failureThreshold: 0,
         failureThresholdType: 'pixel',
       });
 
       // Check that pixelmatch was not called
-      expect(mockPixelMatch).not.toHaveBeenCalled();
+      expect(mockPixelMatch).toHaveBeenCalledWith(
+        expect.any(Object), // buffer data
+        expect.any(Object), // buffer data
+        expect.any(Object), // buffer data
+        expect.any(Number), // image width
+        expect.any(Number), // image height
+        { foo: 'bar', threshold: 0.01 }
+      );
     });
 
     it('should create diff output directory if there is not one already and test is failing', () => {

src/diff-snapshot.js

@@ -19,7 +19,6 @@ const mkdirp = require('mkdirp');
 const pixelmatch = require('pixelmatch');
 const { PNG } = require('pngjs');
 const rimraf = require('rimraf');
-const { createHash } = require('crypto');
 const glur = require('glur');
 const ImageComposer = require('./image-composer');
 
@@ -85,7 +84,6 @@ const shouldUpdate = ({ pass, updateSnapshot, updatePassedSnapshot }) => (
 );
 
 function diffImageToSnapshot(options) {
-  /* eslint complexity: ["error", 12] */
   const {
     receivedImageBuffer,
     snapshotIdentifier,
@@ -147,34 +145,27 @@ function diffImageToSnapshot(options) {
     let diffRatio = 0;
     let diffPixelCount = 0;
 
-    const receivedImageDigest = createHash('sha1').update(receivedImage.data).digest('base64');
-    const baselineImageDigest = createHash('sha1').update(baselineImage.data).digest('base64');
-
-    pass = receivedImageDigest === baselineImageDigest;
-
-    if (!pass) {
-      diffPixelCount = pixelmatch(
-        receivedImage.data,
-        baselineImage.data,
-        diffImage.data,
-        imageWidth,
-        imageHeight,
-        diffConfig
-      );
+    diffPixelCount = pixelmatch(
+      receivedImage.data,
+      baselineImage.data,
+      diffImage.data,
+      imageWidth,
+      imageHeight,
+      diffConfig
+    );
 
-      const totalPixels = imageWidth * imageHeight;
-      diffRatio = diffPixelCount / totalPixels;
-      // Always fail test on image size mismatch
-      if (hasSizeMismatch) {
-        pass = false;
-        diffSize = true;
-      } else if (failureThresholdType === 'pixel') {
-        pass = diffPixelCount <= failureThreshold;
-      } else if (failureThresholdType === 'percent') {
-        pass = diffRatio <= failureThreshold;
-      } else {
-        throw new Error(`Unknown failureThresholdType: ${failureThresholdType}. Valid options are "pixel" or "percent".`);
-      }
+    const totalPixels = imageWidth * imageHeight;
+    diffRatio = diffPixelCount / totalPixels;
+    // Always fail test on image size mismatch
+    if (hasSizeMismatch) {
+      pass = false;
+      diffSize = true;
+    } else if (failureThresholdType === 'pixel') {
+      pass = diffPixelCount <= failureThreshold;
+    } else if (failureThresholdType === 'percent') {
+      pass = diffRatio <= failureThreshold;
+    } else {
+      throw new Error(`Unknown failureThresholdType: ${failureThresholdType}. Valid options are "pixel" or "percent".`);
     }
 
     if (isFailure({ pass, updateSnapshot })) {