Fable.Pyxpecto

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This repository is heavily inspired by Fable.Mocha by the awesome @Zaid-Ajaj.

Inspired by the popular Expecto library for F# and adopts the testList, testCase and testCaseAsync primitives for defining tests.

Fable.Pyxpecto can be used to run tests in Python, JavaScript, TypeScript and .NET! Or use compiler statements to switch between Pyxpecto and keep using Fable.Mocha and Expecto!

Table of Contents

• Fable.Pyxpecto
  • Features
    • Reuse Expecto/Fable.Mocha Tests
    • Pending
    • Focused
    • Sequential Tests
    • Command Line Arguments
  • Install
  • Running tests
    • Language Agnostic
    • With Mocha and Expecto
  • Development
    • Requirements
    • Setup
    • Routines
      • Tests

Features

Reuse Expecto/Fable.Mocha Tests

/// Reuse unit tests from Expecto and Fable.Mocha let tests_basic = testList "Basic" [ testCase "testCase works with numbers" <| fun () -> Expect.equal (1 + 1) 2 "Should be equal" testCase "isFalse works" <| fun () -> Expect.isFalse (1 = 2) "Should be equal" testCase "areEqual with msg" <| fun _ -> Expect.equal 2 2 "They are the same" testCase "isOk works correctly" <| fun _ -> let actual = Ok true Expect.isOk actual "Should be Ok" ]

Pending

Pending tests will not be run, but displayed as "skipped".

ptestCase "skipping this one" <| fun _ -> failwith "Shouldn't be running this test" ptestCaseAsync "skipping this one async" <| async { failwith "Shouldn't be running this test" }

Focused

If there are any focused tests all other tests will not be run and are displayed as "skipped".

👀 Passing the --fail-on-focused-tests command line argument will make the runner fail if focused tests exist. This is used to avoid passing CI chains, when accidently pushing focused tests.

Example py my_focused_tests_file.py --fail-on-focused-tests will fail.

let focusedTestsCases = testList "Focused" [ ftestCase "Focused sync test" <| fun _ -> Expect.equal (1 + 1) 2 "Should be equal" ftestCaseAsync "Focused async test" <| async { Expect.equal (1 + 1) 2 "Should be equal" } ]

Sequential Tests

Actually all tests run with this library will be sequential. The function is only added to comply with Expecto syntax.

💬 Help wanted. I currently have a prototype implementation for parallel tests on a branch. But it breaks collecting run-tests in .NET.

Command Line Arguments

Running any py/ts/js/net code from pyxpecto can be customized with flags:

Fable.Pyxtpecto (F#) Author: Kevin Frey Usage: (python/node/npx ts-node/dotnet run) <path_to_entrypoint> [options] Options: --fail-on-focused-tests Will exit with ExitCode 4 if run with this argument and focused tests are found. --silent Only start and result print. No print for each test. --do-not-exit-with-code Will only return integer as result and not explicitly call `Environment.Exit`. This can be useful to call Pyxpecto tests from foreign test frameworks

These can also be given via:

[<EntryPoint>] let main argv = !!Pyxpecto.runTests [| ConfigArg.FailOnFocused ConfigArg.Silent |] all

Install

From Nuget with:

• paket add Fable.Pyxpecto
• <PackageReference Include="Fable.Pyxpecto" Version="0.0.0" />

Running tests

Language Agnostic

Fable.Pyxpecto does not use any dependencies and tries to support as many fable languages as possible. Check out the multitarget test project to see it fully set up!

open Fable.Pyxpecto // This is possibly the most magic used to make this work. // Js and ts cannot use `Async.RunSynchronously`, instead they use `Async.StartAsPromise`. // Here we need the transpiler not to worry about the output type. #if !FABLE_COMPILER_JAVASCRIPT && !FABLE_COMPILER_TYPESCRIPT let (!!) (any: 'a) = any #endif #if FABLE_COMPILER_JAVASCRIPT || FABLE_COMPILER_TYPESCRIPT open Fable.Core.JsInterop #endif [<EntryPoint>] let main argv = !!Pyxpecto.runTests [||] all

Then run it using:

• .NET: dotnet run
• JavaScript:
  • dotnet fable {rootPath} -o {rootPath}/{js_folder_name}
  • node {rootPath}/{js_folder_name}/Main.js
  • Requirements:
    • nodejs installed.
    • package.json with "type": "module".
    • init with npm init.
    • See: package.json.
• TypeScript:
  • dotnet fable {rootPath} --lang ts -o {rootPath}/{ts_folder_name}
  • npx ts-node {rootPath}/{ts_folder_name}/Main.ts
  • Requirements:
    • possible same as JavaScript.
    • Require tsconfig file, see: tsconfig.json. (💬 Help wanted)
• Python:
  • dotnet fable {rootPath} --lang py -o {rootPath}/{py_folder_name}
  • python {rootPath}/{py_folder_name}/main.py
  • Requirements:

    • python (v>=3.14) executable on your PATH, or replace python with path/to/python.exe.

      Might work with versions as low as 3.12

    • installed fable-library python dependency (version = "5.0.0a17")

With Mocha and Expecto

Use the following syntax to automatically switch between Expecto, Fable.Mocha and Pyxpecto:

#if FABLE_COMPILER_PYTHON open Fable.Pyxpecto #endif #if FABLE_COMPILER_JAVASCRIPT open Fable.Mocha #endif #if !FABLE_COMPILER open Expecto #endif [<EntryPoint>] let main argv = #if FABLE_COMPILER_PYTHON Pyxpecto.runTests [||] all #endif #if FABLE_COMPILER_JAVASCRIPT Mocha.runTests all #endif #if !FABLE_COMPILER Tests.runTestsWithCLIArgs [] [||] all #endif

⚠️ If you want to use Pyxpecto in combination with Fable.Mocha you need to conditionally set Fable.Mocha dependency as shown below. Without this fable will try to transpile Fable.Mocha to python, which will result in errors.

<!-- .fsproj file--> <PackageReference Condition="'$(FABLE_COMPILER_JAVASCRIPT)' == 'true'" Include="Fable.Mocha" Version="2.17.0" />

👀 Everything in curly braces are placeholders

1. Transpile test project to python dotnet fable {path/to/tests} --lang py -o {path/to/tests}/py
2. Run tests python {path/to/tests}/{EntryFileName.py}

Development

Requirements

• uv
  • check with uv --version (Tested with 0.9.13)
• Dotnet SDK
  • check with dotnet --version (Tested with 7.0.306)
• Node
  • check with node --version (Tested with v22)
• npm
  • check with npm --version (Tested with 11.6)

Setup

Run all commands in root.

1. dotnet tool restore
2. npm install

Routines

Tests

./build.cmd runtests

Can be specified to run tests for specific environment.

Switch test project

• ./build.cmd runtestsdotnet
• ./build.cmd runtestsjs
• ./build.cmd runtestspy

Multitarget test project

• ./build.cmd runmtpy
• ./build.cmd runmtjs
• ./build.cmd runmtts
• ./build.cmd runmtnet

Publish

0. Verify all tests pass ./build.cmd runtests
1. Update CHANGELOG.md version with changes.
2. dotnet pack ./src/Fable.Pyxpecto -o ./pkg
3. Upload file from ./pkg to Nuget