feat(diff): increase the maxBuffer to 10MB for the diff process (amer…

…icanexpress#167)

By default, Node's spawnSync has a maxBuffer of 1 MB. This bumps it up
to 10 MB, which should reduce the chance of diffs on large images
failing.

__tests__/integration.spec.js

@@ -306,5 +306,20 @@ describe('toMatchImageSnapshot', () => {
 
       expect(diffExists(customSnapshotIdentifier)).toBe(false);
     });
+
+    it('handles diffs for large images', () => {
+      const largeImageData = fs.readFileSync(fromStubs('LargeTestImage.png'));
+      const largeFailureImageData = fs.readFileSync(fromStubs('LargeTestImageFailure.png'));
+      const customSnapshotIdentifier = getIdentifierIndicatingCleanupIsRequired();
+      // First we need to write a new snapshot image
+      expect(
+        () => expect(largeImageData).toMatchImageSnapshot({ customSnapshotIdentifier })
+      ).not.toThrowError();
+
+      // then test against a different image
+      expect(
+        () => expect(largeFailureImageData).toMatchImageSnapshot({ customSnapshotIdentifier })
+      ).toThrow(/Expected image to match or be a close match/);
+    });
   });
 });

src/diff-snapshot.js

@@ -240,7 +240,11 @@ function runDiffImageToSnapshot(options) {
 
   const writeDiffProcess = childProcess.spawnSync(
     process.execPath, [`${__dirname}/diff-process.js`],
-    { input: Buffer.from(serializedInput), stdio: ['pipe', 'inherit', 'inherit', 'pipe'] }
+    {
+      input: Buffer.from(serializedInput),
+      stdio: ['pipe', 'inherit', 'inherit', 'pipe'],
+      maxBuffer: 10 * 1024 * 1024, // 10 MB
+    }
   );
 
   if (writeDiffProcess.status === 0) {