Impeller Golden Tests

This is the executable that will generate the golden image results that can then be sent to Skia Gold vial the golden_tests_harvester.

Running these tests should happen from //flutter/testing/run_tests.py. That will do all the steps to generate the golden images and transmit them to Skia Gold. If you run the tests locally it will not actually upload anything. That only happens if the script is executed from LUCI.

Example invocation:

./run_tests.py --variant="host_debug_unopt_arm64" --type="impeller-golden"

Currently these tests are only supported on macOS and only test the Metal backend to Impeller.

Adding tests

To add a golden image test, the impeller_golden_tests target must be modified to generate the correct image and modification to its generated digest.json. If a test case is added to golden_tests.cc, for example "GoldenTests.FooBar", that will turn into the golden test "impeller_GoldenTests_Foobar" automatically if the SaveScreenshot() function is used.

The examples in golden_tests.cc use GLFW for rendering the tests, but technically anything could be used. Using the SaveScreenshot() function will automatically update the GoldenDigest::Instance() which will make sure that it is included in the generated digest.json. If that function isn't used the GoldenDigest should be updated manually.