mlh-tsd
v0.14.1
Published
Check TypeScript type definitions
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mlh-tsd
Check TypeScript type definitions. Vanilla tsd but with extra features.
Install
$ npm install mlh-tsd
Overview
This tool lets you write tests for your type definitions (i.e. your .d.ts
files) by creating files with the .test-d.ts
extension.
These .test-d.ts
files will not be executed, and not even compiled in the standard way. Instead, these files will be parsed for special constructs such as expectError<Foo>(bar)
and then statically analyzed against your type definitions.
Usage
Let's assume we wrote a index.d.ts
type definition for our concat module.
declare const concat: {
(value1: string, value2: string): string;
(value1: number, value2: number): string;
};
export default concat;
In order to test this definition, add a index.test-d.ts
file.
import concat from '.';
concat('foo', 'bar');
concat(1, 2);
Running npx tsd
as a command will verify that the type definition works correctly.
Let's add some extra assertions. We can assert the return type of our function call to match a certain type.
import {expectType} from 'mlh-tsd';
import concat from '.';
expectType<string>(concat('foo', 'bar'));
expectType<string>(concat(1, 2));
The tsd
command will succeed again.
We change our implementation and type definition to return a number
when both inputs are of type number
.
declare const concat: {
(value1: string, value2: string): string;
(value1: number, value2: number): number;
};
export default concat;
If we don't change the test file and we run the tsd
command again, the test will fail.
Strict type assertions
Type assertions are strict. This means that if you expect the type to be string | number
but the argument is of type string
, the tests will fail.
import {expectType} from 'mlh-tsd';
import concat from '.';
expectType<string>(concat('foo', 'bar'));
expectType<string | number>(concat('foo', 'bar'));
If we run tsd
, we will notice that it reports an error because the concat
method returns the type string
and not string | number
.
If you still want loose type assertion, you can use expectAssignable
for that.
import {expectType, expectAssignable} from 'mlh-tsd';
import concat from '.';
expectType<string>(concat('foo', 'bar'));
expectAssignable<string | number>(concat('foo', 'bar'));
Top-level await
If your method returns a Promise
, you can use top-level await
to resolve the value instead of wrapping it in an async
IIFE.
import {expectType, expectError} from 'mlh-tsd';
import concat from '.';
expectType<Promise<string>>(concat('foo', 'bar'));
expectType<string>(await concat('foo', 'bar'));
expectError(await concat(true, false));
Test directory
When you have spread your tests over multiple files, you can store all those files in a test directory called test-d
. If you want to use another directory name, you can change it in package.json
.
{
"name": "my-module",
"tsd": {
"directory": "my-test-dir"
}
}
Now you can put all your test files in the my-test-dir
directory.
Custom TypeScript config
By default, tsd
applies the following configuration:
{
"strict": true,
"jsx": "react",
"target": "es2017",
"lib": ["es2017"],
"module": "commonjs",
// The following option is set and is not overridable:
"moduleResolution": "node"
}
These options will be overridden if a tsconfig.json
file is found in your project. You also have the possibility to provide a custom config by specifying it in package.json
:
{
"name": "my-module",
"tsd": {
"compilerOptions": {
"strict": false
}
}
}
Default options will apply if you don't override them explicitly. You can't override the moduleResolution
option.
Assertions
expectType<T>(value)
Check that the type of value
is identical to type T
.
expectNotType<T>(value)
Check that the type of value
is not identical to type T
.
expectAssignable<T>(value)
Check that the type of value
is assignable to type T
.
expectNotAssignable<T>(value)
Check that the type of value
is not assignable to type T
.
expectError(function)
Check if the function call has argument type errors.
expectError<T>(value)
Check if a value is of the provided type T
.
expectDeprecated(value)
Check that value
is marked a @deprecated
.
expectNotDeprecated(value)
Check that value
is not marked a @deprecated
.
Programmatic API
You can use the programmatic API to retrieve the diagnostics and do something with them. This can be useful to run the tests with AVA, Jest or any other testing framework.
import tsd from 'mlh-tsd';
(async () => {
const diagnoser = await tsd();
// Returns the number of tests evaludated.
console.log(diagnoser.numTests)
// Returns the diagnostics if any or just an empty array
console.log(diagnoser.diagnostics);
})();
tsd([options])
Retrieve the type definition diagnostics of the project.
options
Type: object
cwd
Type: string
Default: process.cwd()
Current working directory of the project to retrieve the diagnostics for.
typingsFile
Type: string
Default: ''
Path to the type definitions of the project.
testFiles
type: string[]
default: ['']
An array of test files with their path
License
MIT © Sam Verschueren