• __cases__: each scenario/minimal repo is in a sub-folder of this one
• __templates__: contains the package dependency templates for test cases
• __templates__/default: is the default template
• __tests__: contains the actual tests
• __workdir_symlink__: is created during a test run and is a symbolic link to a subfolder in the temp folder of the OS where all test cases are installed

To run a test case (one of __cases__) in your e2e tests, you must use the configureTestCase(...) helper imported from e2e/__helpers__/test-case.ts:

const testCase = configureTestCase(
    name: string,
    options?: {
        template?: string
        env?: {}
        args?: string[]
    }
)

• name, required: The name of the test case (directory of your case within e2e/__cases__/)
• template, optional: The name of the template to be used (directory of the template within e2e/__template__/)
• env, optional: Extra environment variables to set when running (ie.: {MY_VAR: '1'})
• args, optional: Extra arguments to give to jest when running (ie.: ['--coverage'])

The returned value is an object with those properties and methods:

• testCase.name: name of the case

• testCase.templateName: name of the template (it will resolve it if not given in configureTestCase())

• testCase.workdir: full path to the directory where the tests will be run for that test case (it won't exists until the run() method has been called)

• testCase.run(): will prepare the test case workdir folder and run jest in it, returning an object with these properties:

  • status, number: the status code it exited with
  • stdout, string: the data written to stdout during the run
  • stderr, string: the data written to stderr during the run
  • output, string: the data written to stdout and stderr during the run

  Note 1: The value returned by run() is snapshot friendly (ie.: you can expect(x.run()).toMatchSnapshot(), it'll remove any changing values such as time values)

  Note 2: You can optionally pass the expected status code as the first argument of run(). In the case it's not the correct one, it'll write in the console the actual output so that you can debug the test case.

Bare simple example of using it in your tests:

const testCase = configureTestCase('some-case');
expect(testCase.run().status).toBe(0);

You can find more information on how to create and use templates there.

You run the E2E tests with yarn test:e2e (or npm run test:e2e). What will happen in order is as follow (directories are related to [ts-jest]/e2e path):

1. A bundle (we'll call it [bundle]) will be created for ts-jest using npm pack (yarn pack is buggy).

   The prepublish script will be run, so clean and build (that is why e2e tests are launched before the others, since it's building as part of the process)

2. a sub-folder is created in the main temp dir of the OS, let's refer to it as [e2e-temp]

3. a template directory [e2e-temp]/__templates__/[xxx] is created for each __templates__/[xxx] by copying files

4. npm ci and npm install --save-dev [bundle] will be run in each [e2e-temp]/__templates__/[xxx] directory

   We use npm ci as it's the fastest install way, but it requires a package-lock.json, that is why we need another step to install our bundle from step 1. Doing so in template directories will allow us to link the node modules in real test cases, instead of running npm install for each of them.

5. each test suite under __tests__/**/*.spec.ts are run.

Then within tests, when the configureTestCase(...).run() is called (see how to use configureTestCase), this is what happen:

1. the test case folder is recursively copied from __cases__/[case-name] to [e2e-temp]/[template-name]/[case-name]

2. a node_modules symbolic link is created, targeting its appropriate template's node_modules path ([e2e-temp]/__templates__/[template-name]/node_modules)

   Using templates allow us to install only once the node modules for each template, a template being a kind of "package-set". If the template name is not given in configureTestCase(), the one in e2eTemplate field of __cases__/[case-name]/package.json is used. If this field is not set, the default template is used.

E2E tests being in a temporary folder of the operating system ensure none of the parents would be containing node_modules.

For a concrete example, requiring @babel/core in a test case under [ts-jest]/tests/some-test-case-folder/ would look for @babel/core in [ts-jest]/tests/some-test-case-folder/node_modules/ of course, and if not found will fallback to [ts-jest]/node_modules.

Having the test cases outside of [ts-jest] project's root ensures it won't fallback the resolution of node modules within dev dependencies of ts-jest itself.

Not to mention that using npm pack ensure those tests cases have the same version of ts-jest as the one we would publish on NPM.