Is there any option to set a map of environment variables for a Test task lazily based on a task output (except waiting for the postponed lazy provider migration)?

you could write the variables to a file and configure a

doFirst

action on your test task that reads the file and configures the env variables?

Does it need to be an environment variable? With

getJvmArgumentProviders()

system properties can be passed in lazily (using

listOf("-DpropName=propValue")

. https://github.com/gradle/gradle/blob/v9.2.1/subprojects/core-api/src/main/java/org/gradle/process/JavaForkOptions.java#L168-L175

Just use

val_name = providers.environmentVariable("ENV_VAL_NAME")

Misread it, you want to set the variable. Adam's point about

jvmArgumentProviders

is likely the cleanest way if your app can use System Properties.