Lint contents of nf-test.config

[adamrtalbot]

Description of feature

The nf-test.config file needs to contain the following 3 lines:

• testsDir ".": Make sure tests are relative to root of repository
• workDir System.getenv("NFT_WORKDIR") ?: ".nf-test": Ensure a user-configurable nf-test directory
• configFile "tests/nextflow.config": Use a test specific config

See example for rnaseq: https://github.com/nf-core/rnaseq/blob/99fb7efc9d2b17a7940f745570ff162c04548bc4/nf-test.config

config {
    // Location of nf-tests
    testsDir "."

    // nf-test directory used to create temporary files for each test
    workDir System.getenv("NFT_WORKDIR") ?: ".nf-test"

    // Location of an optional nextflow.config file specific for executing pipeline tests
    configFile "tests/nextflow.config"

    profile "test"
}

We should add linting to this file to make sure the contents are valid for nf-core.