A test framework for ReScript applications.

Installation

npm install zekr

Add to your rescript.json:

{
  "dev-dependencies": ["zekr"]
}

Usage

Write a test file named *.test.res (e.g. MyTests.test.res) that defines one or more suites — you don't call the runner yourself:

open Zekr
let myTests = Suite.make("My Tests", [
  Test.make("addition works", () => {
    Assert.equal(1 + 1, 2)
  }),
  Test.make("strings match", () => {
    Assert.equal("hello", "hello")
  }),
  Test.make("condition is true", () => {
    Assert.isTrue(10 > 5)
  }),
])

Then build and run with the zekr CLI, which discovers every *.test.res file and runs its registered suites automatically:

npm test

That's the recommended workflow. If you'd rather drive the runner yourself — standalone scripts, custom harnesses — see Running suites manually.

API

Zekr is organized as a set of submodules under the top-level Zekr namespace:

Module	Purpose
`Zekr.Test`	Test case factories (`make`, `skip`, `only`, …)
`Zekr.Suite`	Suite factories (`make`, `async`)
`Zekr.Assert`	Assertions (`equal`, `isTrue`, `some`, …)
`Zekr.Runner`	Running suites directly for standalone execution (the CLI is preferred)
`Zekr.Snapshot`	Snapshot testing
`Zekr.DomTesting`	DOM rendering, queries, events, assertions

You can open Zekr to bring the submodules into scope and write Test.make(...), Assert.equal(...), etc.

Creating Tests

// Create a single test
let myTest = Test.make("test name", () => {
  // return Pass or Fail(message)
  Pass
})
// Skip or focus a test
let skipped = Test.skip("wip", () => Pass)
let focused = Test.only("focus me", () => Pass)
// Create a test suite
let mySuite = Suite.make("Suite Name", [test1, test2, test3])

Setup/Teardown Hooks

Add lifecycle hooks directly to your test suites:

// Synchronous hooks
let mySuite = Suite.make(
  "Database Tests",
  [test1, test2, test3],
  ~beforeAll=() => initializeDatabase(),
  ~afterAll=() => closeDatabase(),
  ~beforeEach=() => clearTables(),
  ~afterEach=() => resetState(),
)
// Async hooks
let myAsyncSuite = Suite.async(
  "API Tests",
  [asyncTest1, asyncTest2],
  ~beforeAll=async () => await connectToServer(),
  ~afterAll=async () => await disconnectFromServer(),
  ~beforeEach=async () => await resetMocks(),
  ~afterEach=async () => await cleanup(),
)

All hooks are optional — only provide the ones you need:

let mySuite = Suite.make(
  "My Tests",
  [test1, test2],
  ~beforeEach=() => resetState(),
)

Async Tests with Timeout

Async tests support an optional timeout parameter (in milliseconds). Tests that exceed the timeout will fail automatically. Uncaught exceptions in async tests are also caught and reported as failures.

let myAsyncTests = Suite.async("API Tests", [
  // Test with 5 second timeout
  Test.async("fetches data", async () => {
    let data = await fetchData()
    Assert.equal(data.status, "ok")
  }, ~timeout=5000),
  // Test without timeout (runs until completion)
  Test.async("processes data", async () => {
    let result = await processData()
    Assert.isTrue(result.success)
  }),
])

Assertions

// Check equality
Assert.equal(actual, expected)
Assert.equal(actual, expected, ~message="custom message")
// Check inequality
Assert.notEqual(actual, expected)
// Check boolean conditions
Assert.isTrue(condition)
Assert.isFalse(condition)
// Ordering
Assert.greaterThan(actual, expected)
Assert.lessThan(actual, expected)
Assert.greaterThanOrEqual(actual, expected)
Assert.lessThanOrEqual(actual, expected)
// Collections and strings
Assert.contains(haystack, needle)
Assert.arrayContains(arr, item)
Assert.matches(str, regex)
// Option and result
Assert.some(maybeValue)
Assert.none(maybeValue)
Assert.ok(result)
Assert.error(result)
// Exceptions
Assert.throws(() => someFn())
// Combine multiple results
Assert.combineResults([result1, result2, result3])

Snapshot Testing

Test complex data structures by comparing against stored snapshots:

let snapshotTests = Suite.make("API Response", [
  Test.make("user data matches snapshot", () => {
    let user = {"id": 1, "name": "Alice", "roles": ["admin", "user"]}
    Snapshot.matches(user, ~name="user-data")
  }),
])

On first run, snapshots are created in __snapshots__/. Subsequent runs compare against stored snapshots.

// Configure custom snapshot directory
Snapshot.setDir("tests/__snapshots__")
// Update a snapshot programmatically
Snapshot.update(newValue, ~name="snapshot-name")

Test Filtering

Filter tests by passing environment variables to the zekr CLI:

# Run only tests matching "user"
ZEKR_FILTER="user" zekr
# Skip tests matching "slow"
ZEKR_SKIP="slow" zekr
# Combine filter and skip
ZEKR_FILTER="api" ZEKR_SKIP="integration" zekr

Filtering is case-insensitive and matches against both suite and test names. The same variables work when running suites manually (e.g. ZEKR_FILTER="user" node tests/MyTests.js).

Watch Mode

Automatically re-run tests when files change with the CLI:

zekr --watch

It runs an initial pass, then re-runs only the tests impacted by each change. See Watch mode (--watch) for the full behaviour.

Programmatic watch

If you drive the runner yourself, Runner.watchMode watches paths and re-runs a shell command on each change:

// In a separate watch script (e.g., watch.res)
open Zekr
Runner.watchMode(
  ~testCommand="node tests/MyTests.js",
  ~watchPaths=["src", "tests"],
  ~buildCommand="npx rescript",
)

DOM Testing

Test DOM rendering, user interactions, and element assertions using a built-in jsdom environment. Inspired by Testing Library.

Rendering

open Zekr
let myTests = Suite.make("Login Form", [
  Test.make("renders and accepts input", () => {
    // Render HTML into a jsdom container
    let {container} = DomTesting.render(`
      <form>
        <label for="email">Email</label>
        <input id="email" type="email" value="" />
        <button type="submit">Sign In</button>
      </form>
    `)
    let input = container->DomTesting.Query.getByLabelText("Email")
    DomTesting.Event.typeText(input, "user@example.com")
    let result = DomTesting.Assert.toHaveValue(input, "user@example.com")
    // Clean up the rendered DOM after each test
    DomTesting.cleanup()
    result
  }),
])

Queries

Find elements in the rendered DOM. Each query type comes in three variants:

getBy* — returns the element, throws if not found or if multiple match
queryBy* — returns option<Dom.element>, None if not found
getAllBy* — returns array<Dom.element>, throws if none found

// By text content
container->DomTesting.Query.getByText("Hello World")
container->DomTesting.Query.getByText("hello", ~exact=false)
// By ARIA role (implicit roles from HTML tags are supported)
container->DomTesting.Query.getByRole("button")
container->DomTesting.Query.getByRole("heading", ~level=2)
container->DomTesting.Query.getByRole("button", ~name="Submit")
container->DomTesting.Query.getByRole("checkbox", ~checked=true)
// By test id
container->DomTesting.Query.getByTestId("submit-btn")
// By form attributes
container->DomTesting.Query.getByPlaceholder("Enter your email")
container->DomTesting.Query.getByLabelText("Username")
container->DomTesting.Query.getByDisplayValue("current text")
// By other attributes
container->DomTesting.Query.getByAltText("Company logo")
container->DomTesting.Query.getByTitle("Close")

User Events

Simulate user interactions. Events fire realistic event sequences (pointer, mouse, keyboard, input events).

// Mouse
DomTesting.Event.click(element)
DomTesting.Event.dblClick(element)
DomTesting.Event.hover(element)
DomTesting.Event.unhover(element)
// Keyboard / Text
DomTesting.Event.typeText(input, "Hello World")
DomTesting.Event.clear(input)
// Form controls
DomTesting.Event.check(checkbox)
DomTesting.Event.uncheck(checkbox)
DomTesting.Event.selectOptions(select, ["option-value"])
// Focus
DomTesting.Event.focus(element)
DomTesting.Event.blur(element)
// Low-level custom event dispatch
DomTesting.Event.fire(element, someEvent)

DOM Assertions

All assertions return testResult (Pass or Fail(message)), integrating with zekr's existing assertion system.

// Presence
DomTesting.Assert.toBeInTheDocument(element)
DomTesting.Assert.toNotBeInTheDocument(optionElement)
// Text content
DomTesting.Assert.toHaveTextContent(element, "Hello")
DomTesting.Assert.toHaveTextContent(element, "hello", ~exact=false)
// Attributes and classes
DomTesting.Assert.toHaveAttribute(element, "href")
DomTesting.Assert.toHaveAttribute(element, "href", ~value="/home")
DomTesting.Assert.toNotHaveAttribute(element, "disabled")
DomTesting.Assert.toHaveClass(element, "active primary")
DomTesting.Assert.toNotHaveClass(element, "hidden")
// Visibility and state
DomTesting.Assert.toBeVisible(element)
DomTesting.Assert.toNotBeVisible(element)
DomTesting.Assert.toBeDisabled(element)
DomTesting.Assert.toBeEnabled(element)
// Form values
DomTesting.Assert.toHaveValue(input, "hello")
DomTesting.Assert.toBeChecked(checkbox)
DomTesting.Assert.toNotBeChecked(checkbox)
// Containment
DomTesting.Assert.toContainElement(parent, child)
DomTesting.Assert.toNotContainElement(parent, child)
DomTesting.Assert.toContainHTML(element, "<strong>Bold</strong>")
DomTesting.Assert.toBeEmptyDOMElement(element)
// Style and focus
DomTesting.Assert.toHaveStyle(element, "color", "red")
DomTesting.Assert.toHaveFocus(element)
DomTesting.Assert.toNotHaveFocus(element)

Combining Results

Use Assert.combineResults to check multiple assertions in a single test:

Test.make("form state is correct", () => {
  let {container} = DomTesting.render(`...`)
  let input = container->DomTesting.Query.getByRole("textbox")
  let button = container->DomTesting.Query.getByRole("button")
  let result = Assert.combineResults([
    DomTesting.Assert.toHaveValue(input, ""),
    DomTesting.Assert.toBeEnabled(button),
    DomTesting.Assert.toBeVisible(button),
  ])
  DomTesting.cleanup()
  result
})

Running tests with the CLI

Zekr ships a zekr binary that discovers and runs your test files. Build with ReScript first, then run zekr:

By default it scans the current directory for files ending in .test.res (e.g. Color.test.res) and runs each compiled file in its own Node process.

Options

Flag	Alias	Default	Description
`--pattern <suffix>`	`-p`	`.test.res`	Filename suffix to match
`--dir <path>`	`-d`	`.`	Directory to scan
`--watch`	`-w`		Watch for changes and re-run only impacted tests
`--help`	`-h`		Show usage

Watch mode (`--watch`)

zekr --watch runs a full pass, then watches the scan directory and re-runs only the tests impacted by each change:

Change a test file (Foo.test.res) → only that test file re-runs.
Change a source module (Foo.res) → every test that references Foo (Foo.something or open Foo) re-runs.

Run your compiler in watch mode alongside it so tests always run against freshly built output:

zekr reacts to compiled output (.js, .res.mjs, …), not raw .res saves, so it never runs stale code. Rapid change bursts are debounced into a single run. Press Ctrl+C to stop.

When any test fails, watch mode prints a Failing tests summary at the end of the run — grouping the failing test names under each file — so you don't have to scroll back through the output to find what broke:

zekr: 1 files, 0 passed, 1 failed
Failing tests:
  tests/Math.test.res
    ✗ addition is broken
    ✗ handles negatives

Config file

Instead of flags, add a zekr.json at your project root:

{ "pattern": ".test.res", "dir": "." }

Flags override zekr.json, which overrides the defaults. node_modules, lib, .git, and dot-directories are skipped. If a matched source has no compiled output, zekr reports it and exits non-zero — run rescript first.

Custom ReScript `suffix`

Zekr works whatever suffix your rescript.json sets (.res.mjs, .mjs, .bs.js, .js, …). ReScript compiles the whole build graph — including zekr's own sources — with that suffix, so the CLI discovers the matching compiled test files and runs each one against the Runner compiled with the same suffix. This keeps the internal suite registry a single shared instance; without it, tests compiled to Foo.test.res.mjs would register into a different module instance than the runner read, and the CLI would report zero tests (a false green).

Test Coverage

Generate test coverage reports on your ReScript source files using c8 (V8 native coverage). Since ReScript doesn't support sourcemaps natively, Zekr includes a sourcemap generator that maps compiled JavaScript back to .res files.

Setup

Install the required dev dependencies:

npm install --save-dev c8 source-map

Add coverage scripts to your package.json:

{
  "scripts": {
    "precoverage": "rescript && node node_modules/zekr/scripts/generate-sourcemaps.mjs src",
    "coverage": "c8 zekr"
  },
  "c8": {
    "include": ["src/**/*.js"],
    "reporter": ["text", "html"],
    "report-dir": "coverage",
    "all": true
  }
}

Run coverage:

npm run coverage

The text report shows coverage on .res files with line numbers pointing to your ReScript source, and the HTML report (in coverage/) renders the original ReScript code with highlighted coverage.

See the Coverage documentation for more details.

Running suites manually

The zekr CLI is the recommended way to run tests. The Runner API is still available for standalone execution — running a compiled test file directly with node, or building a custom harness — in which case the test file calls the runner itself:

open Zekr
let mySuite = Suite.make("My Tests", [
  Test.make("addition works", () => Assert.equal(1 + 1, 2)),
])
// Run a single suite
Runner.runSuite(mySuite)
// Run multiple suites
Runner.runSuites([mySuite])
// Async variants
await Runner.runAsyncSuite(myAsyncSuite)
await Runner.runAsyncSuites([suite1, suite2])

node tests/MyTests.js

Under the CLI you don't add these calls — the CLI discovers *.test.res files and runs their registered suites for you.

License

MIT