README

jest-preset-spfx

A Jest preset configuration for SharePoint Framework (SPFx) projects.

NOTE: This preset does not contain any support for SPFx projects that utilize React.

See the related packages jest-preset-spfx-react15 & jest-preset-spfx-react16 if you are leveraging React in your SPFx projects.

Installation

Install the desired Jest preset using your package manager of choice:
```
npm install @voitanos/jest-preset-spfx --save-dev
```
This will install @types/jest, ts-jest & identity-obj-proxy as dependencies in your project.

The postinstall script will verify you have a ./config/jest.config.json file and update your package.json scripts with two scripts for running Jest tests with this configuration: test & test:watch.

If the configuration file is not present, it will create it. If it is present, it will verify the minimal properties.

IMPORTANT: Make sure you install the version of the preset that matches the version of TypeScript you're using in your project. See Installing specific preset versions for details on how to determine the correct version.

NOTE: A specific version of ts-jest is used to support the SPFx supported version of TypeScript as more current versions of ts-jest require newer versions of TypeScript that is not yet supported by SPFx.
Install the specified version of Jest for your preset version. See Installing specific preset versions for guidance on picking the correct preset version.

When the you install the preset, it will output to the console the version of Jest you need to install that the installed version of the ts-jest transformer uses. Look for the following statement in the console:
```
ACTION REQUIRED: Install Jest v25.5.4 by executing the following command in the console:
   npm install jest@25.5.4 --save-dev --save-exact
```
Execute the command displayed in the console to install the required version of Jest in your project.

Installing specific preset versions

Figuring out the correct matrix of package versions to install can be challenging. This mostly comes down to TypeScript.

SPFx projects are written in TypeScript but Jest defaults to testing JavaScript files. We use the popular ts-jest transformer that converts TypeScript files to JavaScript as Jest executes it's tests. Each version of ts-jest is written to match a specific version of TypeScript and Jest.

But no worries! We've done the hard part of figuring out what combinations of versions you need.

Determine the TypeScript version of your project

First, determine the version of TypeScript your SPFx project uses:

Open the package.json file in your SPFx project.
Within the devDependencies object, look for the package that starts with the name @microsoft/rush-stack-compiler-.

This package is the bridge to a specific version of TypeScript. The TypeScript version is indicated by the last part of the name of the package.

For example, consider the following entry in the package.json file:
```
{
  ...
  "devDependencies": {
    "@microsoft/rush-stack-compiler-2.9": "0.6.8",
    ...
  }
}
```
This SPFx project is using TypeScript v2.9.

Determine the matching Jest preset version

The next step is to determine the corresponding version of the Jest preset that is configured with the version of TypeScript in your project.

The Jest preset NPM package contains distribution tags that are used to alias specific published versions of the package. We use them to indicate which version is built for a specific version of TypeScript.

Get a list of all distribution tags by executing the following command:
```
npm info @voitanos/jest-preset-spfx
```
Locate the matching TypeScript version. The previous command will write the package information to the console as well as a list of the published distribution tags:
```
dist-tags:
latest: 1.2.2             next: 1.3.0-beta.b385582  ts2.9: 1.2.2
```
From this output, you can see three tags:
- latest: the most current stable version of the NPM package that's been published
- next: the next version of the NPM package, usually a beta and used for testing
- ts2.9: the version built for TypeScript v2.9

Install a specific Jest preset package version

Using the information above, install the specific Jest preset package:

npm install @voitanos/jest-preset-spfx@ts2.9 --save-dev --save-exact

NOTE: Pay close attention to the console output as you'll likely have at least one additional step (look for ACTION REQUIRED). The console will also contain information about changes applied to your project to support tests.

Validating Installation

To validate a successful install, do one of the following two things:

Option 1: Add example tests

Copy the folder examples from the installed package (also found here in the source repo) into the project's src folder.
Execute Jest to run the tests:
```
npm test
```
Observe four (4) passing tests.

Option 2: Create your own test

Add a new file SampleTests.spec.ts to the ./src/webparts folder with the following code:

import 'jest';

test('1+1 should equal 2', () => {
  const result = 1+1;
  expect(result).toBe(2);
});

Execute Jest to run the tests:
```
npm test
```
Observe a single (1) passing test.

How it works

This package contains a base Jest configuration that your project will inherit. It does this by using the preset property to @voitanos/jest-preset-spfx in the jest.config.json file.

References

Package.json NPM scripts

Two scripts are added to the package.json scripts section:

test: Run Jest and specify the configuration file to use: npm test.
test:watch: Run Jest and specify the configuration file to use, but run in watch mode so when files change, it will automatically re-run the tests: npm run test:watch.

Jest preset configuration for SPFx

The following preset is used for SPFx projects:

Explanation of select configuration properties above: jest-preset.json

collectCoverage, coverageDirectory, collectCoverageFrom & coverageReporters: collects code coverage statistics and generates associated reports in the ./temp/test folder
moduleNameMapper:
- when Jest sees a request for a CSS/SCSS file in the source files, it effectively ignores it using the identity-obj-proxy package
- when jest sees a request for en-us.json, it is provided a helper path to find the file
testMatch: all tests found either in a special __tests__ folder or within the src folder with the following names will be found:
- *.spec.ts
- *.spec.tsx
- *.spec.js
- *.spec.jsx
- *.test.ts
- *.test.tsx
- *.test.js
- *.test.jsx
transform: the Jest preprocessor will transpile all TypeScript files to JavaScript before running the tests.

Usage no npm install needed!