(test): add initial test harness and one simple test

- ensure that width/height of canvas are trimmed down after drawing a
  purple rectangle in the center

- add test script that uses jest
  - (ci): change CI to run test and test:pub
- configure jest and babel-jest
  - add coverage/ directory to gitignore
  - add babel-jest@23 for Babel 6 support
    - and configure it for .js files due to a jest bug
  - add .babelrc to configure babel-jest
    - can't use .babelrc.js as babel-jest@23 doesn't support it
      - jestjs/jest#5324
    - can't use .babelrc for babel-loader (have to duplicate config)
      because babel-loader@6 has some bugs with it and babel-loader@7
      doesn't support webpack@1
      - babel/babel-loader#552

(deps): add jest, babel-jest, and canvas-prebuilt to devDeps
- add canvas-prebuilt@1 to support jest's jsdom v11
  - canvas is used by jsdom for, well, canvas interactions

.babelrc

@@ -0,0 +1,3 @@
+{
+  "presets": ["es2015"]
+}

.gitignore

@@ -2,6 +2,7 @@ npm-debug.log*
 node_modules/
 
 build/
+coverage/
 *.tgz
 
 .DS_Store

.travis.yml

@@ -2,4 +2,5 @@ language: node_js
 # default is apparently 0.10.48
 node_js: '10.16.0'
 
-script: npm run test:pub
+script: npm test
+after_script: npm run test:pub

jest.config.js

@@ -0,0 +1,6 @@
+module.exports = {
+  transform: {
+    // use babel-jest@23 for babel@6 support (https://github.com/facebook/jest/issues/8230#issuecomment-479470547)
+    '\\.js$': require.resolve('babel-jest')
+  }
+}

package.json

@@ -29,16 +29,19 @@
     "lint": "standard index.js",
     "build:watch": "webpack --watch -d",
     "build:prod": "webpack -p",
-    "test": "echo \"Error: no test specified\" && exit 1",
+    "test": "jest",
     "test:pub": "npm run build:prod && npm pack",
     "pub": "npm run build:prod && npm publish",
     "changelog": "changelog-maker"
   },
   "devDependencies": {
     "@agilgur5/changelog-maker": "^3.0.0",
     "babel-core": "^6.0.14",
+    "babel-jest": "^23.6.0",
     "babel-loader": "^6.0.0",
     "babel-preset-es2015": "^6.6.0",
+    "canvas-prebuilt": "^1.6.11",
+    "jest": "^24.9.0",
     "webpack": "^1.12.2"
   }
 }

test/index.spec.js

@@ -0,0 +1,17 @@
+import trimCanvas from '../index.js'
+
+describe('trimCanvas', () => {
+  it('should trim whitespace', () => {
+    const canvas = document.createElement('canvas')
+    const ctx = canvas.getContext('2d')
+    canvas.width = 1000
+    canvas.height = 1000
+
+    ctx.fillStyle = 'purple'
+    ctx.fillRect(450, 450, 100, 100) // 100x100 purple box in center
+
+    trimCanvas(canvas)
+    expect(canvas.width).toBe(100)
+    expect(canvas.height).toBe(100)
+  })
+})