jest-runner-tsd
v6.0.0
Published
Run your TypeScript type tests using Jest
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jest-runner-tsd
Run your TypeScript type tests using Jest.
Note: the jest-runner-tsd
is using tsd-lite
instead of tsd
. Both of them have the same type testing logic, but tsd-lite
makes it easier to test projects written in TypeScript (or types generated by your library).
Most important differences (for the full list see tsd-lite
repo):
tsd-lite
has no additional rules or checks;jest.config
is used to discover test files;tsconfig.json
provides configuration for TS compiler. For details see Configuration section;- the type assertions must be imported from
tsd-lite
package.
Install
yarn add --dev jest-runner-tsd @tsd/typescript
# or
npm install --save-dev jest-runner-tsd @tsd/typescript
Remember to install @tsd/typescript
package. It is a required peer dependency.
Note that @tsd/typescript
will be used to compile type tests. Generally it is recommended to match versions of @tsd/typescript
and typescript
in a project, but you may choose to test on different version too.
Configuration
Jest
First of all, you should configure Jest to discover your test files. For example, if the files have .test.ts
suffix and live inside __typetests__
directories, set up jest.config.tsd.js
like this:
module.exports = {
displayName: {
color: 'blue',
name: 'types',
},
runner: 'jest-runner-tsd',
testMatch: ['**/__typetests__/*.test.ts'],
};
TS Compiler
Your test files will be compiled using the TypeScript compiler (similar to tsc
), but, instead of emitting JS code, tsd-lite
will analyze types and diagnostics returned by the compiler.
To compile each test file, tsd-lite
will read the nearest tsconfig.json
and will pass the configuration to the compiler. Hence, you may have a configuration for the whole project, or a group of test files, or just a particular test file.
For example, if your project already includes a tsconfig.json
in the root directory, but you prefer to have different configuration for testing, simply add another tsconfig.json
to a directory with the test files. It may override or extend your root configuration.
Tip: run yarn tsc -p path/to/__typetests__ --showConfig
to print the configuration which applies to the test files.
Note: if tsconfig.json
is not found, the compiler will fall back to the default configuration.
Optionally Strict
Just like TypeScript, tsd-lite
is optionally strict. In contrary, the vanilla tsd
is strict by default. If you are migrating your test suite, remember to set "strict": true
in tsconfig.json
.
import { expectType } from 'tsd-lite';
declare const loggedInUsername: string;
const users = [
{ name: 'Oby', age: 12 },
{ name: 'Heera', age: 32 },
];
const loggedInUser = users.find(u => u.name === loggedInUsername);
expectType<number>(loggedInUser.age);
The assertion in this example fails with "strict": true
, but passes with "strict": false
.
Writing Tests
Let's say you defined a JsonObject
type:
// JsonObject.ts
type JsonValue = string | number | boolean | JsonObject | Array<JsonValue>;
export interface JsonObject {
[key: string]: JsonValue;
}
It is relatively complex, so it is worth adding a type test to prevent mistakes and regression in the future:
// __typetests__/JsonObject.test.ts
import { expectAssignable, expectNotAssignable } from 'tsd-lite';
import type { JsonObject } from '../JsonObject.js';
expectAssignable<JsonObject>({
caption: 'test',
count: 100,
isTest: true,
location: { name: 'test', start: [1, 2], valid: false, x: 10, y: 20 },
values: [0, 10, 20, { x: 1, y: 2 }, true, 'test', ['a', 'b']],
});
expectNotAssignable<JsonObject>({
filter: () => {},
});
Tip: For the full list of type testing assertions see the documentation of tsd-lite
.
Running Tests
If all is set, simply run yarn jest --config jest.config.tsd.js
command. Or better include a script in package.json
:
"scripts": {
"test:types": "jest --config jest.config.tsd.js"
}
License
MIT © Jest Community