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Eric Peterson

December 23, 2017

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Today's featured module is a TestBox module that introduces snapshot testing capabilities to TestBox. If you've avoided testing your legacy applications, come see how [TestBox Snapshots](https://www.forgebox.io/view/testbox-snapshots) can get you started.

TestBox Snapshots

What is snapshot testing?

Snapshot testing is the latest craze. Popularized by Facebook’s Jest testing framework, snapshot testing is a simple way to add regression testing to your application.

Snapshots are useful for making sure the data passed in does not change unexpectedly. Snapshots aren't meant to replace other types of testing and assertions, but rather are another tool for helping you sleep at night knowing your application is performing as it should.

Setup

To get started with snapshot testing in TestBox, install the testbox-snapshots module from ForgeBox. Then add the matchers in your beforeAll method.

function beforeAll() {
    super.beforeAll();
    addMatchers( "testbox-snapshots.SnapshotMatchers" );
}

You can then assert that snapshots match using the toMatchSnapshot method.

it( "should display the home page", function() {
	var event = execute( event = "Main.index", renderResults = true );
	expect( event.getRenderedContent() ).toMatchSnapshot();
} );

Note: there is no notToMatchSnapshot method.

Here's the flow for how the matcher works:

  1. It checks if a snapshot has been generated for this spec. If not, it fails the test and suggests you generate a snapshot.

  2. If the updateSnapshots url flag is passed, the snapshot will be created or updated with the new value and the test will pass.

  3. If a snapshot exists and the updateSnapshots url flag is not passed, it passes only if the value passed in matches the snapshot.

Better Diffing

For more precise changes, make sure to include the optional java library in your test's load paths (this.javaSettings). It produces a diff of the files instead of just outputting the contents in their entirety. You can enable this by including the following in your tests/Application.cfc:

this.javaSettings = {
    loadPaths = [ "testbox-snapshots/lib" ],
    reloadOnChange = false
};

Wrap Up

Want more information on snapshot testing with TestBox? You can check out my own blog post about the subject, or Jason Steinshouer's two-part series on the topic (here and here).

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