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rescript-test

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library8.0.0jsnpmunverified

rescript-test is a lightweight and performant test framework designed specifically for ReScript projects. Currently at version 8.0.0, it provides a native ReScript API for writing unit and integration tests, leveraging ReScript's type system for robust assertions. It integrates directly into the ReScript build pipeline, running compiled `.bs.js` files. The framework offers core testing primitives like `test`, `testAsync`, and flexible `assertion` functions, alongside utilities for setup/teardown and optional DOM simulation via JSDOM. It aims to provide a straightforward, type-safe testing experience tailored for the ReScript ecosystem, differentiating itself from general JavaScript test runners by its deep integration with ReScript's language features. It appears to be actively maintained, with updates typically correlating with ReScript compiler releases.

testing
npm install rescript-test
package ↗
INSTALL
IMPORT
SIG · RESCRIPT-TEST
R
rescript-test
testingjavascriptv8.0.0
Install
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Import
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Disk
—
Pass rate
0/ 6
Env Coverage0 / 6
glibc
18–22
musl
18–22
Install & Compatibility
Where this runs
tested against v? · npm install
Install × environment matrix
Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux
musl
node 18–226 runs
build_error
glibc
node 18–226 runs
build_error
Code
Verified usage

Verified import paths — ran on the pinned version, not inferred.

retest CLI
✓ npx retest 'test/**/*.bs.js'
✗ import { retest } from 'rescript-test'; // CLI is not a JS module
The `retest` command-line interface (CLI) is the primary way to execute tests written with `rescript-test`. The actual testing API (`test`, `assertion`, etc.) is consumed directly within ReScript source files (`.res`) using `open Test` and does not expose direct JavaScript module imports for these functions. Attempting to import or require it in JavaScript code will result in module not found errors for the testing API itself.
Test module (ReScript)
✓ open Test
✗ import { Test } from 'rescript-test'; // This is ReScript syntax, not JS.
Within ReScript source files, the `Test` module is made available via `open Test` at the top of your test file, similar to importing a namespace in other languages. This exposes functions like `test`, `assertion`, `throws`, etc., for use in your ReScript code.

Demonstrates how to install `rescript-test`, configure `bsconfig.json`, write a basic ReScript test file with custom assertions, and execute it using the `retest` CLI.

yarn add --dev rescript-test # Add to bsconfig.json: # { # "bs-dev-dependencies": [ # "rescript-test" # ] # } # Create test/MyTest.res // test/MyTest.res open Test let intEqual = (~message=?, a: int, b: int) => assertion(~message?, ~operator="intEqual", (a, b) => a === b, a, b) test("Basic integer equality", () => { let actual = 1 + 1 let expected = 2 intEqual(~message="1 + 1 should be 2", actual, expected) }) test("Async operation test", () => { // In a real scenario, this would involve a Promise or callback // For simplicity, showing a synchronous pass. pass() }) # Run the tests npx retest 'test/**/*.bs.js'
Debug
Known issues
breakingThis package is a ReScript-native testing framework and requires the ReScript compiler (version ^12.0.1 or higher) as a peer dependency. Using it with significantly older ReScript versions will lead to compilation errors or unexpected runtime behavior.
fix
Ensure your project's `rescript` dependency matches or exceeds `^12.0.1`. Update ReScript compiler version if necessary via `npm install rescript@latest`.
affects: <8.0.0
breakingThe `retest` CLI requires Node.js version 20.0.0 or higher. Running it with older Node.js versions will result in execution failures.
fix
Upgrade your Node.js runtime environment to version 20.0.0 or newer. Use a version manager like `nvm` to easily switch Node.js versions.
affects: <8.0.0
gotchaThe `rescript-test` API (e.g., `test`, `assertion`) is designed for use within ReScript source files (`.res`). There are no direct JavaScript module exports for these testing utilities. Attempts to `import` or `require` them directly in JavaScript or TypeScript files will fail.
fix
Write your tests in ReScript (`.res` files) and compile them to JavaScript. Then, use the `retest` CLI to run the compiled `.bs.js` test files.
affects: >=1.0.0
gotchaTo enable DOM testing functionality, the `--with-dom` flag must be explicitly passed to the `retest` CLI. This feature relies on `jsdom` which is an optional peer dependency; ensure it's installed if you intend to use DOM testing.
fix
Install `jsdom` as a dev dependency (`yarn add --dev jsdom`) and execute tests with `npx retest --with-dom 'test/**/*.bs.js'`.
affects: >=1.0.0
Errors
Common errors & fixes
Error: Cannot find module 'rescript-test/lib/js/src/Test.bs.js'
The ReScript compiler cannot locate the `rescript-test` module, likely due to incorrect `bsconfig.json` configuration or missing installation.
fix
Ensure `rescript-test` is listed in your `bs-dev-dependencies` array within `bsconfig.json` and that `yarn add --dev rescript-test` has been run successfully.
retest: command not found
The `retest` executable is not in your system's PATH, or `rescript-test` is not installed.
fix
Install `rescript-test` as a dev dependency (`yarn add --dev rescript-test`). If installed, try running with `npx retest ...` to execute the local package binary.
Type Error: The module 'test.bs.js' could not be loaded due to a type mismatch in ReScript
A mismatch between the expected types by `rescript-test` and the types provided in your ReScript test code, or using an assertion with incompatible types.
fix
Review your ReScript test code for type errors highlighted by the ReScript compiler. Ensure arguments passed to assertions like `intEqual` or `stringEqual` match their defined types. Recompile your ReScript code (`npm run res:build` or `yarn res:build`) before running tests.
Assertion Failed: Char code should match
A custom assertion logic within your ReScript test file returned `false`, indicating an expected condition was not met.
fix
Examine the test case where the failure occurred. Debug the values being compared against your assertion logic to understand why the condition `(a, b) => a === b` or your custom comparator returned `false`.
Upgrade
Version history
8.0.0latest on npm
Audit
Dependencies
rescriptrequiredPeer dependency for the ReScript compiler, essential for compiling and running tests.
noderequiredEngine requirement for running the CLI and compiled tests.
jsdomoptionalOptional dependency used for simulating a browser DOM environment when running tests with the `--with-dom` flag.
Agent activity
2 hits · last 30 days
node
2
Resources
packagehttps://www.npmjs.com/package/rescript-test ↗
rescript-test — npm install rescript-test · libregistry