swift snapshot testing + cli

Very small addition to https://github.com/pointfreeco/swift-snapshot-testing to record snapshot from environment value passed in cli of set in scheme.

In xcode scheme go to scheme > edit scheme > run > arguments and add SNAPSHOT_TESTING_UPDATE_TESTS true there to update all tests

A global envIsRecording is also availble

that one you can use in de record of an assert. This is needed for InlineSnapshot testing as with the new withSnapshotTesting(record:diffTool:operation:) the recording of inline does not work with the proposed wrap around invoke test.

Use case

To update tests in a swift package from commandline rather then in code.

export SNAPSHOT_TESTING_UPDATE_TESTS=true &&swift test --generate-linuxmain

Discussion

I wonder if it would be a nice addition and I am dissussing it here pointfreeco/swift-snapshot-testing#457 (comment)