inline-test-ppx

A PPX to write inline tests in ReScript.

// Math.res
let sum = (a, b) => {
  a + b
}

@inline_test
test("adds 1 + 2 to equal 3", () => {
  expect(sum(1, 2)).toBe(3);
});

The test will be erased in compilation phase for production builds.

Installation

We provide an NPM package with prebuilt binaries.

yarn add @dialo/inline-test-ppx
# Or
npm install --save @dialo/inline-test-ppx

And add the PPX in your bsconfig.json file:

{
  "ppx-flags": [
    "ppx-flags": ["inline-test-ppx"]
  ]
}

Usage

1. Install the testing framework of your choice (like jest, zora, rescript-test or other)

2. Write some inline tests:

   // Math.res
   let sum = (a, b) => {
     a + b
   }
   
   @inline_test
   Jest.test("adds 1 + 2 to equal 3", () => {
     expect(sum(1, 2)).toBe(3);
   });

   Note: our PPX assumes that the testing framework is designed similarly to jest or zora. I.e. that tests are simply defined as top level expressions in arbitrary files. At the time of writing this readme we are not aware of testing frameworks for rescript that are designed differently.

3. Make test runner aware of the tests. All tests are indirectly accessible through lib/bs/__inline_test.*:

   Jest

   In your jest config

   testMatch: [
     "lib/bs/__inline_test.*.cjs", // use .mjs if you have es6 output configured in bsconfig
     // other test locations ...
   ]
   

   Zora (with pta):

   // scripts in package.json
   "test": "NODE_ENV=test pta 'lib/bs/__inline_test.*.cjs'" // add other locations as you see fit
   

   Please note that in order for tests to be run, NODE_ENV has to be set to test, which is done by default by Jest but not by some other frameworks.

   Others

   Other frameworks usually have similar configurations which allow you to point to the location of JavaScript files containing case. In the case of our ppx all tests are referenced by artifacts located in lib/bs/ prefixed with __inline_test.

4. Compile your sources with INLINE_TEST=1 to compile the tests

   // scripts in package.json
   "watch": "INLINE_TEST=1 rescript build  -with-deps -w"
   

   Caveat

   Beaware that now all of the modules which contain inline tests will have inline tests present in .js artifacts. If you run:

   INLINE_TEST=0 yarn rescript build
   

   your modules will not be recompiled. In order to get rid of the testing code in js files clean the project first using:

   yarn rescript clean
   

   and then recompile them with the INLINE_TEST environment variable simply undefined or defined as 0 or false.

How it works

The PPX compiles any top level expression in a module conditionally based on the existence of INLINE_TEST env variable in the build environment. It means that:

@inline_test
Js.Console.log("hello")

will be only compiled by rescript if the variable is present. Otherwise it's simply ommited and not present in the resulting .js file.

Contributing

Take a look at our Contributing Guide.