Some useful extensions for expect.js

expect_js_extensions.js

// This allows us to assert that an object has the specified key.
// Alternatively we could say expect(obj.key).toExist()
// but the problem is that if the test fails, we only see: "Expected undefined to exist"
// and we don't know which property is missing.
expect.extend({
  toHaveProperty(prop){
    expect.assert(prop in this.actual, "Expected object to have property %s", prop)
  },
});

// Building on previous extension, this lets us assert
// that an object has all keys in the specified list.
expect.extend({
  toHaveProperties(propList){
    propList.forEach(function(prop) {
      expect(this.actual).toHaveProperty(prop)
    }, this)
  }
});