indoorvivants / snapshot-testing   0.0.5

GitHub

SBT plugin and runtime for snapshot testing

Scala versions: 3.x 2.13 2.12
Scala.js versions: 1.x
Scala Native versions: 0.4
sbt plugins: 1.0

sbt-snapshots Scala version support

snapshots-testing

This is a micro library to aid with snapshot testing.

The meat of the project is actually in build tool integration - I wanted to have an experience similar to that of Insta with its Cargo integration. Currently only SBT is supported, but Mill support can be added easily, as the project is already structured in a way that favours that.

One of the goals was being able to work with Scala.js and Scala Native - so the Scala.js portion of the runtime includes small Node.js bindings to the fs module for filesystem operations.

The runtime is published for 2.12, 2.13, 3 and JVM, JS, Native.

Installation (SBT)

To add the plugin to your SBT build:

  1. addSbtPlugin("com.indoorvivants.snapshots" % "sbt-snapshots" % "VERSION") to your project/plugins.sbt (see VERSION on the badge above)

  2. In the project where you would like to use snapshot testing, add these settings:

    .settings(
      snapshotsPackageName          := "example",
      snapshotsIntegrations         += SnapshotIntegration.MUnit // if using MUnit
    )
    .enablePlugins(SnapshotsPlugin)

    Package name is the only required setting, because the plugin will generate a source file that ties build-time filesystem locations with runtime test execution.

The library provides no diffing capabilities, instead delegating that task to the test framework of choice.

Usage

SBT tasks:

  • snapshotsCheck - interactively accept modified snapshots (if there are any)
  • snapshotsAcceptAll - accept all modified snapshots
  • snapshotsDiscardAll - discard all snapshot changes

SBT settings:

  • snapshotsIntegrations - list of test framework integrations to generate in test sources

    Instead of providing a separate dependency for each test framework, the plugin generates a single-file integration. This helps avoid the dependency hell of incompatible framework versions. It might seem weird at first, because it is, but I believe it's the only way to stay sane.

  • snapshotsPackageName - package name to use for generated file

  • snapshotsForceOverwrite - if set to true, snapshot assertions won't fail the tests, but instead they will directly overwrite snapshot contents with the new value.

    It is particularly useful in a setting where you want to only check snapshots on CI, but always update them locally without having to explicitly accept.

    Recommended configuration is therefore snapshotsForceOverwrite := !sys.env.contains("CI") - or whatever way you can detect that your code is running in CI

Sample MUnit tests

You can see what the workflow looks like by

  1. Modifying the sample test above
  2. Running example/test and observing a failure
  3. Running example/snapshotsCheck and accepting a diff
  4. Running example/test again and it should succeed
  5. The snapshot file will be changed on disk

Here's the same workflow in video format:

video.mp4

Scala.js

The snapshots runtime will only run under Node.js (or any runtime where require("node:fs") import can succeed).

To make sure module import is enabled, you should ensure you're using the correct module kind - for example commonJS:

scalaJSLinkerConfig ~= (_.withModuleKind(ModuleKind.CommonJSModule))