Custom matchers, provided by the behavior-driven development framework Jasmine, is a great feature for testing JavaScript code. Custom Matchers helps to group multiple catch checking which makes the test cases clean and self explanatory.
Let’s look at an example that I tried recently
Here is a Calculator.js file:
1: var Calculator = function () { };
2: 3: Calculator.prototype.add = function (a, b) {
4: return a + b;
5: }; 6: 7: Calculator.prototype.divide = function (a, b) {
8: return a / b;
9: };One of the test scenarios that I would like to try is to check whether the result of the method is in a particular range. The test method will look like this with existing matchers.
1: describe('Calculator', function () {
2: var calc;
3: 4: beforeEach(function () {
5: calc = new Calculator();
6: }); 7: 8: it('should be able to add 1 and 1', function () {
9: expect(calc.add(1, 1)).toBe(2); 10: }); 11: 12: it('should be able to divide 6 by 2', function () {
13: expect(calc.divide(6, 2)).toBe(3); 14: }) 15: 16: it('should be able to divide a rational number', function () {
17: expect(calc.divide(1, 3)).toBeLessThan(0.34); 18: expect(calc.divide(1, 3)).toBeGreaterThan(0.3); 19: }) 20: });But you can replace the existing matchers with a custom matcher like this.
1: describe('Calculator', function () {
2: var calc;
3: 4: beforeEach(function () {
5: calc = new Calculator();
6: 7: jasmine.addMatchers({8: toBeBetween: function (util, customEqualityTesters) {
9: return {
10: compare: function (actual, a, b) {
11: var result = {};
12: result.pass = actual >= a && actual <= b;13: return result;
14: } 15: } 16: } 17: }); 18: }); 19: 20: it('should be able to add 1 and 1', function () {
21: expect(calc.add(1, 1)).toBe(2); 22: }); 23: 24: it('should be able to divide 6 by 2', function () {
25: expect(calc.divide(6, 2)).toBe(3); 26: }) 27: 28: it('should be able to divide a rational number', function () {
29: expect(calc.divide(1, 3)).toBeBetween(0.3, 0.34); 30: }) 31: });You can reuse custom matchers to make the test cases clear and more simple.
What are some scenarios that you use custom matchers?
