Added a few snapshot tests

.eslintrc.js

@@ -1,17 +1,16 @@
 module.exports = {
   'env': {
     'browser': true,
-    'node': true
+    'node': true,
+    'mocha': true,
+    'es2017': true
   },
   'extends': 'eslint:recommended',
   'globals': {
     'Uint8Array': false,
     'define': false,
     'Float32Array': false
   },
-  'plugins': [
-    'mocha'
-  ],
   'rules': {
     'indent': [
       'error',

package.json

@@ -16,7 +16,6 @@
     "eslint": "^7.32.0",
     "eslint-config-standard": "^16.0.3",
     "eslint-plugin-import": "^2.24.1",
-    "eslint-plugin-mocha": "^9.0.0",
     "eslint-plugin-node": "^11.1.0",
     "eslint-plugin-promise": "^5.1.0",
     "mocha": "^9.1.0",

test/matches-snapshot.js

@@ -0,0 +1,65 @@
+const fs = require('fs');
+const PNG = require('pngjs').PNG;
+const path = require('path');
+
+const snapshotsPath = 'snapshots';
+
+function assertMatchesImage(actual, imageFilename) {
+  if(!imageFilename.endsWith('.png')) {
+    console.log('throwing');
+    throw new Error('imageFilename must end in .png');
+  }
+  let fileBuffer;
+  try {
+    fileBuffer = fs.readFileSync(path.join(snapshotsPath, imageFilename));
+  }
+  catch (_) {
+    writeImageSnapshot(actual, imageFilename);
+    return;
+  }
+  const png = PNG.sync.read(fileBuffer);
+  if (actual.data.length * 4 !== png.data.length) {
+    throw new Error('Expected actual.length to match png.data.length');
+  }
+  const identical = actual.data.every((value, i) => value == png.data[i*4]);
+  if(!identical) {
+    console.log(png.data);
+    writeImageSnapshot(actual, imageFilename.replace('.png', '.error.png'));
+    throw new Error('expected data to be identitcal');
+  }
+
+}
+exports.assertMatchesImage = assertMatchesImage;
+
+function writeImageSnapshot(actual, imageFilename) {
+  const png = new PNG({
+    colorType: 0,
+    inputColorType: 0,
+    bitDepth: 16,
+    width: actual.width,
+    height: actual.height,
+    inputHasAlpha: false,
+  });
+  if (actual.data.length*4 !== png.data.length) {
+    console.warn(actual.data.length, png.data.length);
+    throw new Error('Expected actual.data.length to match png.data.length');
+  }
+  png.data.forEach((_,i, a) => a[i] = (i%4==3) ? 255 : actual.data[(i/4)|0]);
+
+  fs.writeFileSync(path.join(snapshotsPath, imageFilename), PNG.sync.write(png.pack(), {colorType: 0} ));
+}
+
+function sampleFunctionToImageData(f, width, height) {
+  let imageData = {
+    width,
+    height,
+    data: new Uint8ClampedArray(width*height)
+  };
+  for(let y = 0; y < height; y++) {
+    for (let x = 0; x < width; x++) {
+      imageData.data[y*width+x] = f(x, y);
+    }
+  }
+  return imageData;
+}
+exports.sampleFunctionToImageData = sampleFunctionToImageData;

test/simplex-noise-test.js

@@ -1,8 +1,7 @@
-/* global describe, it, beforeEach */
-
-var SimplexNoise = require('../simplex-noise');
-var Alea = require('alea');
-var assert = require('chai').assert;
+const SimplexNoise = require('../simplex-noise');
+const Alea = require('alea');
+const assert = require('chai').assert;
+const {assertMatchesImage, sampleFunctionToImageData} = require('./matches-snapshot.js');
 
 describe('SimplexNoise', function() {
   function getRandom() {
@@ -25,6 +24,12 @@ describe('SimplexNoise', function() {
         assert.equal(aTable[i], i);
       }
     });
+    it('matches snapshot', function() {
+      var table = SimplexNoise._buildPermutationTable(getRandom());
+
+      const actual = {width: 16, height: 16, data: new Uint8ClampedArray(table)};
+      assertMatchesImage(actual, 'permutationTable.png');
+    });
   });
 
   describe('constructor', function() {
@@ -96,6 +101,10 @@ describe('SimplexNoise', function() {
       it('should return similar values for similar inputs', function() {
         assert(Math.abs(simplex.noise2D(0.1, 0.2) - simplex.noise2D(0.101, 0.202)) < 0.1);
       });
+      it('should match snapshot', function() {
+        const actual = sampleFunctionToImageData((x,y)=>simplex.noise2D(x/10,y/10)*128+128, 64, 64);
+        assertMatchesImage(actual, 'noise2D.png');
+      });
     });
 
     describe('noise3D', function() {
@@ -121,6 +130,10 @@ describe('SimplexNoise', function() {
       it('should return similar values for similar inputs', function() {
         assert(Math.abs(simplex.noise3D(0.1, 0.2, 0.3) - simplex.noise3D(0.101, 0.202, 0.303)) < 0.1);
       });
+      it('should match snapshot', function() {
+        const actual = sampleFunctionToImageData((x,y)=>simplex.noise3D(x/10,y/10,(x+y)/2)*128+128, 64, 64);
+        assertMatchesImage(actual, 'noise3D.png');
+      });
     });
 
     describe('noise4D', function() {
@@ -150,6 +163,10 @@ describe('SimplexNoise', function() {
             simplex.noise4D(0.101, 0.202, 0.303, 0.404)
           ) < 0.1);
       });
+      it('should match snapshot', function() {
+        const actual = sampleFunctionToImageData((x,y)=>simplex.noise4D(x/10,y/10,x/4,y/3)*128+128, 64, 64);
+        assertMatchesImage(actual, 'noise4D.png');
+      });
     });
   });
 });