Testing Your Deno Apps With Mocha

import add from "./add.ts";
import { expect } from "https://deno.land/x/expect@v0.2.1/mod.ts";

Deno.test("should add two numbers", () => {
  expect(add(1, 2)).toEqual(3);
});

/**
 * First we import Mocha and it's type definitions.
 */
// @deno-types="https://unpkg.com/@types/mocha@7.0.2/index.d.ts"
import "https://unpkg.com/mocha@7.2.0/mocha.js";
/**
 * Here I'm using the Deno `expect` library, but you can use
 * any assertion library - including Deno's std testing library.
 * See: https://deno.land/std/testing
 */
import { expect } from "https://deno.land/x/expect@v0.2.1/mod.ts";

/**
 * Callback on completion of tests to ensure Deno exits with
 * the appropriate status code. 
 */
function onCompleted(failures: number): void {
  if (failures > 0) {
      Deno.exit(1);
  } else {
      Deno.exit(0);
  }
}

/**
 * Browser based Mocha requires `window.location` to exist.
 */
(window as any).location = new URL("http://localhost:0");

/**
 * In order to use `describe` etc. we need to set Mocha to `bdd`
 * mode.
 * 
 * We also need to set the reporter to `spec` (though other options
 * are available) to prevent Mocha using the default browser reporter
 * which requires access to a DOM.
 */
mocha.setup({ ui: "bdd", reporter: "spec" });

/**
 * Ensure there are no leaks in our tests.
 */
mocha.checkLeaks();

/**
 * Our example function under test
 */
function add(a: number, b: number): number {
  return a + b;
}

/**
 * We write our tests as usual!
 */
describe("add", () => {
  it("should add two positive numbers correctly", () => {
    expect(add(2, 3)).toEqual(5);
  });
});

/**
 * And finally we run our tests, passing the onCompleted function
 * hook and setting some globals.
 */
mocha.run(onCompleted).globals(["onerror"])

$ deno run ./mocha.ts

This browser lacks typed array (Uint8Array) support which is required by `buffer` v5.x. Use `buffer` v4.x if you require old browser support.


  add
    ✓ should add two positive numbers correctly


  1 passing (3ms)

describe("add", () => {
  it("should add two positive numbers correctly", () => {
    expect(add(2, 3)).toEqual(10); // Should fail!
  });
});

$ deno run ./mocha.ts

This browser lacks typed array (Uint8Array) support which is required by `buffer` v5.x. Use `buffer` v4.x if you require old browser support.


  add
    1) should add two positive numbers correctly


  0 passing (47ms)
  1 failing

  1) add
       should add two positive numbers correctly:
     AssertionError: expect(actual).toEqual(expected)

-   5
+   10
      at applyMatcher (https://deno.land/x/expect@v0.2.1/expect.ts:102:23)
      at Proxy.<anonymous> (https://deno.land/x/expect@v0.2.1/expect.ts:109:15)