Testing TypeScript with Mocha

Typescript is set up and there's a function simpleGreeting defined in src/greetings.ts

We've installed Mocha and Chai, as well as their types.
npm install --save-dev mocha @types/mocha chai @types/chai

• Mocha is the test runner.
• Chai is the assertion library we've chosen to use for our tests.

We've also installed ts-node, which will be used to compile typescript on-the-fly.
npm install ts-node

Adding tests and running them

We've added a unit test for simpleGreeting in test/unit/greetings.spec.ts

We set up package.json so that npm test will run our tests.

"scripts": {
    "test": "mocha --config test/runners/mocha/.mocharc.jsonc"
},

The mocha configuration file .mocharc.jsonc has been set up to find our tests and run test/runners/mocha/init.js.

The project compiles typescript into something other than commonjs modules. Node doesn't play nicely with other formats, so we've added a separate tsconfig.json just for mocha, which init.js feeds into ts-node.

Without that separate tsconfig, we'd get an error like this:

SyntaxError: Cannot use import statement outside a module

Running npm test should output something like this:

  simpleGreeting
    √ should say hello


  1 passing (8ms)

Mocking

We installed ts-mockito.
npm install --save-dev ts-mockito

Some contrived things have been added to src/ to be used as an example for mocking.

• targetedGreeting
• INamed
• MyComplicatedDomainModel

We wrote a unit test for targetedGreeting in greetings.spec.ts and used ts-mockito to mock MyComplicatedDomainModel.