Writing mocha tests with style - OOP style:

import { suite, test, slow, timeout } from "mocha-typescript";
@suite class Hello {
    @test world() { }
}

• Summary
  • Test UI
  • Watcher
  • Thanks To
• Setting Up
  • Adding Mocha-TypeScript to Existing Project
  • Setting up New Project With Custom UI
  • Setting Up Dev Test Watcher
• Test UI API
  • Declarative Suites and Tests
  • Generated Suites and Tests
  • Before and After Actions
  • Async Tests, Before and After Actions
  • Skipped and Only Suite and Tests
  • Timing - Timeout, Slow
• Extending Test Behavior
  • Accessing the Mocha Context Within Class Methods
  • Skipping Tests In Suite After First Failure - skipOnError

The test interface provides support for mocha's built-in tdd, bdd: describe/suite, it/test, timeout, slow, it.only and it.skip; as well as TypeScript decorators based test UI for classes. You can mix and match:

import { suite, test, slow, timeout } from "mocha-typescript";
suite("one", () => {
    test("test", () => {});
});
@suite class Two {
    @test method() {}
}

The mocha-typescript comes with a watcher script that runs the TypeScript compiler in watch mode, and upon successful compilations runs the mocha tests, concatinating the output of both. This in combination with the support for "only":

@suite class One {
    @test.only method1() {}
    @test mothod2() {}
}

Allows for rapid development of both new functionality and unit tests.

Please note, the built in mocha watcher should work with mocha-typescript UI and the awesome-typescript-loader.

• Haringat for the async support in before and after methods.
• godart for taking the extra step to support non-default test file paths.

If you allready have an npm package with mocha testing integrated just install mocha-typescript:

npm i mocha-typescript --save-dev

Then require the mocha-typescript in your test files and you will be good to go:

import { suite, test, slow, timeout } from "mocha-typescript";
@suite class Two {
    @test method() {}
}

Create a folder, cd in the folder, npm init, npm install:

npm init
npm install mocha typescript mocha-typescript @types/mocha source-map-support --save-dev

Edit the package.json and set the sripts section to:

  "scripts": {
    "test": "tsc && mocha",
    "watch": "mocha-typescript-watch"
  },

Add a tsconfig.json file with settings similar to:

{
    "compilerOptions": {
        "target": "es6",
        "module": "commonjs",
        "experimentalDecorators": true,
        "lib": [ "es6" ]
    }
}

Create tests folder and add tests/mocha.opts file.

--ui mocha-typescript
--require source-map-support/register
test/tests.js

• Sets the mocha-typescript as custom ui
• Optionally require the source-map-support/register to have typescript stack traces for Errors
• Optionally provide test files list, point to specific dist fodler, or skip this to use mocha's defaults Add your first test file tests/tests.ts:

// Reference mocha-typescript's global definitions:
/// <reference path="../node_modules/mocha-typescript/globals.d.ts" />

@suite(timeout(3000), slow(1000))
class Hello {
    @test world() {
    }
}

From that point on, you could either:

npm test
npm run watch

To run the tests once manually or run all tests. Keep in mind you can use add .only to run a single test.

There is a watcher script in the package, that runs tsc -w process and watches its output for successful compilation, upon compilation runs a mocha process.

You will need a tsconfig.json, and at least test.ts mocha entrypoint.

Install mocha, typescript and mocha-typescript as dev dependencies (required):

npm install mocha typescript mocha-typescript --save-dev

Add the following npm script to package.json:

  "scripts": {
    "dev-test-watch": "mocha-typescript-watch"
  },

And run the typescript mocha watcher from the terminal using npm run dev-test-watch.

You can use the watcher with plain describe, it functions. The decorator based interface is not required for use with the watcher.

The mocha-typescript-watch script is designed as a command line tool. You can provide the arguments in the package.json's script. In case you are not using the default test.js file as entrypoint for mocha, you can list the test suite files as arguments to mocha-typescript-watch and they will be passed to mocha. For example:

  "scripts": {
    "dev-test-watch": "mocha-typescript-watch -p tsconfig.test.json -o mocha.opts dist/test1.js dist/test2.js"
  },

For complete list with check ./node_modules/.bin/mocha-typescript-watch --help:

Options:
  -p, --project  Path to tsconfig file or directory containing tsconfig, passed
                 to `tsc -p <value>`.                    [string] [default: "."]
  -t, --tsc      Path to executable tsc, by default points to typescript
                 installed as dev dependency. Set to 'tsc' for global tsc
                 installation.
                         [string] [default: "./node_modules/typescript/bin/tsc"]
  -o, --opts     Path to mocha.opts file containing additional mocha
                 configuration.          [string] [default: "./test/mocha.opts"]
  -m, --mocha    Path to executable mocha, by default points to mocha installed
                 as dev dependency.
                           [string] [default: "./node_modules/mocha/bin/_mocha"]
  -g, --grep     Passed down to mocha: only run tests matching <pattern>[string]
  -f, --fgrep    Passed down to mocha: only run tests containing <string>
                                                                        [string]
  -h, --help     Show help                                             [boolean]

Please note that the methods and decorators used below are introduced through importing from the mocha-typescript module:

import { suite, test, slow, timeout } from "mocha-typescript";

Or by installing mocha-typescript as custom mocha test UI.

Declaring suites is done using the @suite decorator and tests within the suite using the @test decorator:

@suite class Suite {
    @test test1() {}
}

When used without parameters, the names are infered from the class and method name. Complex names can be provided as arguments to the @suite or @test decorator:

@suite("A suite")
class Suite {
    @test("can have tests") {}
    @test "typescript also supports this syntax for method naming"() {}
}

Mocha's simple interface is very flexible when test have to be dynamically generated. If tests for classes have to be generated dinamically here is an example:

[{ title: "google", url: "www.google.com" },
 { title: "github", url: "www.github.com" }
].forEach({title, url} => {
    @class(`Http ${title}`) OAuthTests {
        @test login() {}
        @test logout() {}
    }
});

By default, before and after test actions are implemented with instance and static before and after methods. The static before and after methods are invoked before the suite and after the suite, the instance before and after methods are infvoked before and after each test method.

@suite class Suite {
    static before() { /* 1 */ }
    before() { /* 2, 5 */ }
    @test one() { /* 3 */ }
    @test one() { /* 6 */ }
    after() { /* 4, 7 */ }
    static after() { /* 8 */ }
}

The methods that accept a done callback or return a Promise are considered async similar and their execution is similar to the one in mocha.

• For done, calling it without params marks the test as passed, calling it with arguments fails the test.
• For returned Promise, the test passes is the promise is resolved, the test fails if the promise is rejected.

@suite class Suite {
    @test async1(done) {
        setTimeout(done, 1000);
    }
    @test async2() {
        return new Promise((resolve, reject) => setTimeout(resolve, 1000));
    }
    @test async async3() {
        // async/await FTW!
        await something();
    }
}

Marking a test as pending or marking it as the only one to execute declaratively is done using @suite.skip, @suite.only, @test.skip or @test.only similar to the mocha interfaces:

@suite.only class SuiteOne {
    @test thisWillRun() {}
    @test.skip thisWillNotRun() {}
}
@suite class SuiteTwo {
    @test thisWillNotRun() {}
}

The signatures for the skip and only are the same as the suite and test counterpart so you can switch between @suite.only(args) and @suite(args) with ease.

If running in watch mode it may be common to focus a particular test file in your favourite IDE (VSCode, vim, whatever), and mark the suite or the tests you are currently developing with only so that the mocha-typescript watcher would trigger just the tests you are focused on. When you are ready, remove the only to have the watcher execute all tests again.

Controlling the time limits, similar to the it("test", function() { this.slow(ms); /* ... */ }); is done using suite or test traits, these are modifiers passed as arguments to the @suite() and @test() decorators:

@suite(slow(1000), timeout(2000))
class Suite {
    @test first() {}
    @test(slow(2000), timeout(4000)) second() {}
}

The slow and timeout traits were initially working as decorators (e.g. @suite @timeout(200) class Test {}), but this behavior may be dropped in future major versions as it generates too much decorators that cluter the syntax. They are still useful though for setting timeouts on before and after methods (e.g. @suite class Test { @timeout(100) before() { /* ... */ }}).

There are various aspects of the suites and tests that can be altered via the mocha context. Within the default mocha 'BDD' style this is done through the callback's this object. That object is exposed to the TypeScript decorators based UI through a field decorated with the @context decorator:

@suite class MyClass {
  @context mocha; // Set for instenace methods such as tests and before/after
  static @context mocha; // Set for static methods such as static before/after (mocha bdd beforeEach/afterEach)
  after() {
    this.mocha.currentTest.state;
  }
}

In functional testing it is sometimes fine to skip the rest of the suite when one of the tests fail. Consider the case of a web site tests where the login test fail and subsequent tests that depend on the login will hardly pass. This can be done with the skipOnError suite trait:

@suite(skipOnError)
class StockSequence {
    @test step1() {}
    @test step2() { throw new Error("Failed"); }
    @test step3() { /* will be skipped */ }
    @test step4() { /* will be skipped */ }
}