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ReScript bindings forJest

NOTE: TheNPM package has moved to@glennsl/rescript-jest. Remember to update bothpackage.json ANDbsconfig.json.

• bs-jest is rebranded as rescript-jest
• rescript-jest depends on Rescript 9.1.4, Jest 27.3.1 and @ryyppy/rescript-promise 2.1.0.
• Starting from Jest 27.0.0 jest-jasmine was replaced by jest-circus changing the semantics for before and after hooks.afterAllAsync andafterAllPromise hooks now time-out consistent with the behavior ofbeforeAllAsync andbeforeAllPromise in version 0.7.0 of bs-jest.beforeAllAsync andbeforeAllPromise also now behave consistently with 'afterAllAsync andafterAllPromise when included in skipped test suites.
• rescript-jest API now uses data-first semantics throughout and usesrescript-promise in place ofJs.Promise.
• usefakeTimers() binding updated to address changes in the Jest fake timer API (useFakeTimer(~implementation=[#legacy|#modern], ()))
• Deprecated BuckleScript@bs.send.pipe bindings were converted to rescript@send bindings.
• All tests have been updated to reflect semantic and behavioral changes.
• Babel modules have been added as dev dependencies to make generated bs-jest bindings available in ES6 module format.
• Babel and Jest config files are included illustrating how to transform ES6 modules for Jest.

To generate ES6 bindings for your project, update bsconfig.json

"suffix":".mjs","package-specs":{"module":"ES6","in-source":true},

Then add@babel/core,@babel/preset-env andbabel-jest packages to your project. Also, add babel.config.js

module.exports={presets:[['@babel/preset-env',{targets:{node:'current'}}]],"plugins":[]}

Finally, add minimal jest.config.js

module.exports={moduleFileExtensions:["js","mjs",],testMatch:["**/__tests__/**/*_test.mjs","**/__tests__/**/*_test.bs.js",],transform:{"^.+\.m?js$":"babel-jest"},transformIgnorePatterns:["node_modules/(?!(rescript)/)"],

Update testMatch, transform and transformIgnorePatterns settings depending on where your tests are stored, and other dependenies of your project that may need to be transformed to ES6 format.

Most of what's commonly used is very stable. But the more js-y parts should be considered experimental, such as mocking and some of the expects that don't transfer well, or just don't make sense for testing idiomatic Reason/OCaml code but could be useful for testing js interop.

• Global: Fully implemented and tested, apart fromrequire.*
• Expect: Mostly implemented. Functionality that makes sense only for JS interop have been moved toExpectJs. Some functionality does not make sense in a typed language, or is not possible to implement sensibly in Rescript.
• Mock Functions: Experimental and unsafe implementation, very much in flux. The Jest bindings will most likely be relegated to theMockJs module as it's very quirky to use with native code. A separate native from-scratch implementation might suddenly appear asMock.
• The Jest Object: Fake timers are fully implemented and tested. Mock functionality has been moved toJestJs. It's mostly implemented, but experimental and largely untested.
• Snapshotting: Expect functions exist and work, but there's currently no way to implement custom snapshot serializers.

openJest;describe("Expect", ()=> {openExpect;test("toBe", ()=>expect(1+2)->toBe(3))});describe("Expect.Operators", ()=> {openExpect;open!Expect.Operators;test("==", ()=>expect(1+2)===3)  });

Seethe tests for more examples.

npm install --save-dev @glennsl/rescript-jest

or

yarn install --save-dev @glennsl/rescript-jest

Then add@glennsl/rescript-jest tobs-dev-dependencies in yourbsconfig.json:

{  ..."bs-dev-dependencies":["@glennsl/rescript-jest"]}

Then add__tests__ tosources in yourbsconfig.json:

"sources":[{"dir":"src"},{"dir":"__tests__","type":"dev"}]

Put tests in a__tests__ directory and use the suffix*test.res/ (Make sure to use valid module names. e.g.<name>_test.res is valid while<name>.test.res is not). When compiled they will be put in a__tests__ directory underlib, with a*test.bs.js suffix, ready to be picked up when you runjest. If you're not already familiar withJest, seethe Jest documentation.

One very important difference from Jest is that assertions are not imperative. That is,expect(1 + 2) -> toBe(3), for example, will not "execute" the assertion then and there. It will instead return anassertion value which must be returned from the test function. Only after the test function has completed will the returned assertion be checked. Any other assertions will be ignored, but unless you explicitly ignore them, it will produce compiler warnings about unused values.This means there can be at most one assertion per test. But it also means there must be at least one assertion per test. You can't forget an assertion in a branch, and think the test passes when in fact it doesn't even test anything. It will also force you to write simple tests that are easy to understand and refactor, and will give you more information about what's wrong when something does go wrong.

At first sight this may still seem very limiting, and if you write very imperative code it really is, but I'd argue the real problem then is the imperative code. There are however some workarounds that can alleviate this:

• Compare multiple values by wrapping them in a tuple:expect((this, that)) -> toBe((3, 4))
• Use thetestAll function to generate tests based on a list of data
• Usedescribe and/orbeforeAll to do setup for a group of tests. Code written in Rescript is immutable by default. Take advantage of it.
• Write a helper function if you find yourself repeating code. That's what functions are for, after all. You can even write a helper function to generate tests.
• If you're still struggling, make an issue on GitHub or bring it up in Discord. We'll either figure out a good way to do it with what we already have, or realize that something actually is missing and add it.

For the moment, please refer toJest.resi.

• bs-jest-dom - Custom matchers to test the state of the DOM

If you encounter the errorSyntaxError: Cannot use import statement outside a module, it may be that you are mixinges6 andcommonjs modules in your project. For example, this can happen when you are building a React project since React builds are always in ES6. To fix this, please do the following:

• Make sure yourbsconfig.json compiles"es6" or"es6-global":

"package-specs": {"module":"es6",  }

• Installesbuild-jest throughyarn ornpm as adevDependency.
• Build your Rescript project with deps:rescript build -with-deps.
• Add this to your Jest config (orjest of yourpackage.json):

{"transform": {"^.+\\.jsx?$":"esbuild-jest"  },"transformIgnorePatterns": ["<rootDir>/node_modules/(?!(rescript|@glennsl/rescript-jest)/)"]}

• The property"transformIgnorePatterns" is an array of strings. Either you do some regex or organize them in an array.Please make sure all folders innode_modules involving compiled .res/.ml/.re files and the like such asrescript or@glennsl/rescript-jest are mentioned in the aforementioned array.

This problem is also addressed inIssue #63.

git clone https://github.com/glennsl/rescript-jest.gitcd rescript-jestnpm install

Then build and run tests withnpm test, start watchers forrescriptandjest withnpm run watch:rescript andnpm run watch:jest respectively. Installscreen to be able to usenpm run watch:screen to run both watchers in a single terminal window.

• [BREAKING] Bump required rescript to 11.1.x, uncurried mode requires MockJs.fn to be applied with explcicit currying.
• Worked around bug in rescript 11 curried mode where@uncurry causes an extra param which changes Jest behaviour, by replacing@uncurry with(. ).

• [BREAKING] Bump required rescript to 10.1.x
• Remove unnecessary dependency on@ryyppy/rescript-promise

• AddedtestAllPromise.

• AddedJest.setSystemTime.

• [BREAKING] Removed the unnecessarily verbose generated namespace.

• Moved repository fromglennsl/bs-jest toglennsl/rescript-jest
• Renamed published package to@glennsl/rescript-jest
• [BREAKING] Converted source code to ReScript, hence will no longer work with versions of BuckleScript that lack ReScript support.
• [BREAKING] As of Jest 27.0.0, Jest-Circus replaces Jest-Jasmine by default leading to change in behavior of async and Promise before and after hooks.
• [BREAKING] As the|> operator is deprecated in Recript 9.x, all APIs now use data-first (->) semantics.

• [BREAKING] Actually removedtoThrowException,toThrowMessage andtoThrowMessageRe as they relied on assumptions about BuckleScript internals that no longer hold.

• AddedExpect.toContainEqual
• Updated to Jest 26.5.2
• Upgraded bs-platform to 8.3.1

• AddedExpect.toMatchInlineSnapshot

• Updated to Jest 25.1.0

• AddedTodo.test

• Updated jest to 24.3.1
• Fixed jest warnings not to return anything fromdescribe callbacks by explicitly returningundefined (otherwise BuckleScript will return something else like(), which is represented as0)
• Fixed several newly uncovered uncurrying issues caused by surprise breaking changes in BuckleScript (Thanks again, Bob!)
• AddedJest.advanceTimersByTime, which is basically just an alias ofJest.runTimersToTime

• AddedExpect.not__ for transitional compatibility with Reason syntax change of "unkeywording"not by mangling it intonot_, andnot_ intonot__ and so on.

• Made uncurrying explicit forafterAllPromise too.

• Made uncurrying explicit to fix a breaking change in implicit uncurrying frombs-platform 4.0.7 (Thanks Bob!)

• Removed some optimizations on skipped tests that Jest 23 suddenly started objecting to (#30)

• AddedMockJs.new0,new1 andnew2
• Addedtimeout argument totestAsync andtestPromise functions
• AddedbeforeEachAsync,beforeEachPromise,afterEachAsync andafterEachPromise
• AddedbeforeAllAsync,beforeAllPromise,afterAllAsync andafterAllPromise

• Moved repository fromreasonml-community/bs-jest toglennsl/bs-jest
• Renamed NPM package frombs-jest to@glennsl/bs-jest

• AddedtoThrowException
• Fixed an issue with custom Runner implementation shadowing the globaltest function from jest
• Fixed a typo in the js boundary ofnot_ |> toBeLessThanEqual

• Removed deprecations
• AddedtestAll,Only.testAll,Skip.testAll that generates tests from a list of inputs
• Fixed type signature offail
• AddedexpectFn