Providing a custom comparison method

There are many scenarios where

You can leverage the TestifyConfiguration.compareMethod configuration function property for this purpose.

To configure a custom capture method, provide a function that conforms to the CompareMethod signature.

CompareMethod is called with the baseline and current bitmaps and expects a boolean result. If you return true, the bitmaps are considered to be the same and the comparison succeeds. If you return false, the bitmaps are considered different and the comparison fails.

typealias CompareMethod = (baselineBitmap: Bitmap, currentBitmap: Bitmap) -> Boolean

tip

Before writing your own comparison method, consider that Testify provides multiple built-in mechanisms to customize the comparison of bitmaps. You can easily increase the matching tolerance or exclude a region from the comparison.

Please also see Accounting for platform differences for more insight into handling unintended differences in your rendering.

You can customize the algorithm used to compare the captured bitmap against the baseline and use this to define a variety of custom comparison algorithms such as allowing a tolerance, or excluding certain values from the comparison.

Ignore differences example

In this example, we build a very simple ComporeMethod, ignoreDifferences(), which will ignore all differences found in your images.

ScreenshotTestRule

@ScreenshotInstrumentation
@Test
fun ignoreDifferences() {

    /**
     * Define a simple comparison method that ignores all differences between the bitmaps by always returning true
     */
    fun ignoreDifferences(baselineBitmap: Bitmap, currentBitmap: Bitmap) = true

    rule
        .setViewModifications {
            // Set background to a random color
            val color = "#${Integer.toHexString(Random.nextInt(0, 16581375)).padStart(6, '0')}"
            it.setBackgroundColor(Color.parseColor(color))
        }
        .configure { compareMethod = ::ignoreDifferences }
        .assertSame()
}

ScreenshotScenarioRule

@ScreenshotInstrumentation
@Test
fun ignoreDifferences() {

    /**
     * Define a simple comparison method that ignores all differences between the bitmaps by always returning true
     */
    fun ignoreDifferences(baselineBitmap: Bitmap, currentBitmap: Bitmap) = true

    launchActivity<TestHarnessActivity>().use { scenario ->
        rule
            .withScenario(scenario)
            .setViewModifications {
                // Set background to a random color
                val color = "#${Integer.toHexString(Random.nextInt(0, 16581375)).padStart(6, '0')}"
                it.setBackgroundColor(Color.parseColor(color))
            }
            .configure { compareMethod = ::ignoreDifferences }
            .assertSame()
    }
}