TypeScript Unit Testing jest (ts-jest)
Example
jest is painless JavaScript testing framework by Facebook, with ts-jest can be used to test TypeScript code.
To install jest using npm run command
npm install --save-dev jest @types/jest ts-jest typescript
For ease of use install jest as global package
npm install -g jest
To make jest work with TypeScript you need to add configuration to package.json
//package.json
{
...
"jest": {
"transform": {
".(ts|tsx)": "<rootDir>/node_modules/ts-jest/preprocessor.js"
},
"testRegex": "(/__tests__/.*|\\.(test|spec))\\.(ts|tsx|js)$",
"moduleFileExtensions": ["ts", "tsx", "js"]
}
}
Now jest is ready.
Assume we have sample fizz buz to test
//fizzBuzz.ts
export function fizzBuzz(n: number): string {
let output = "";
for (let i = 1; i <= n; i++) {
if (i % 5 && i % 3) {
output += i + ' ';
}
if (i % 3 === 0) {
output += 'Fizz ';
}
if (i % 5 === 0) {
output += 'Buzz ';
}
}
return output;
}
Example test could look like
//FizzBuzz.test.ts
/// <reference types="jest" />
import {fizzBuzz} from "./fizzBuzz";
test("FizzBuzz test", () =>{
expect(fizzBuzz(2)).toBe("1 2 ");
expect(fizzBuzz(3)).toBe("1 2 Fizz ");
});
To execute test run
jest
In output you should see
PASS ./fizzBuzz.test.ts
✓ FizzBuzz test (3ms)
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 1.46s, estimated 2s
Ran all test suites.
Code coverage
jest supports generation of code coverage reports.
To use code coverage with TypeScript you need to add another configuration line to package.json.
{
...
"jest": {
...
"testResultsProcessor": "<rootDir>/node_modules/ts-jest/coverageprocessor.js"
}
}
To run tests with generation of coverage report run
jest --coverage
If used with our sample fizz buzz you should see
PASS ./fizzBuzz.test.ts
✓ FizzBuzz test (3ms)
-------------|----------|----------|----------|----------|----------------|
File | % Stmts | % Branch | % Funcs | % Lines |Uncovered Lines |
-------------|----------|----------|----------|----------|----------------|
All files | 92.31 | 87.5 | 100 | 91.67 | |
fizzBuzz.ts | 92.31 | 87.5 | 100 | 91.67 | 13 |
-------------|----------|----------|----------|----------|----------------|
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 1.857s
Ran all test suites.
jest also created folder coverage which contains coverage report in various formats, including user friendly html report in coverage/lcov-report/index.html
