assertScreenshot

Perform visual regression testing of your application against existing screenshots

The assertScreenshot command takes a screenshot and matches it against a known good image, performing a visual regression test.

The assertion will fail if the comparison image is too dissimilar, or doesn't exist.

Syntax

- assertScreenshot: splash.png

or

- assertScreenshot:
    path: screen.png
    cropOn:
      id: banner
    thresholdPercentage: 98

Parameters

Parameter	Type	Description
path	String	Path to the reference screenshot that the current screen will be compared against. Can be a JavaScript expression. Was likely created by a takeScreenshot invocation in a previous run.
cropOn	Element Selector	Optional. A selector to narrow the screenshot before comparison. The comparison screenshot must also have been cropped. For a complete list of all available selectors, see the Selectors documentation.
thresholdPercentage	Number	Optional. Percentage match required to pass this assertion. Default is 95. Can be a variable or a JavaScript expression, as long as it resolves to a number.
label	String	Optional. A message to display when executing the evaluation.

Usage Examples

Assert against a reference screenshot

This example compares the current screen against splash.png, using the default threshold of 95%.

- assertScreenshot: splash.png

Set the threshold from a variable

The threshold is interpolated before the comparison runs, so you can tune it per environment or per device without editing the Flow.

appId: com.example.app
env:
  THRESHOLD_PERCENTAGE: 80
---
- assertScreenshot:
    path: ./screenshot.png
    thresholdPercentage: ${THRESHOLD_PERCENTAGE}

The value must resolve to a number. If it resolves to something else — an empty string from an unset variable, for example — the assertion fails with Invalid thresholdPercentage for assertScreenshot rather than falling back to the default.