Apply suggestions from code review

Author: maxulysse

tests/nextflow.config

@@ -9,6 +9,7 @@
 params.modules_testdata_base_path   = 's3://ngi-igenomes/testdata/nf-core/modules/'
 params.pipelines_testdata_base_path = 's3://ngi-igenomes/testdata/nf-core/pipelines/rnaseq/3.15/'
 params.hisat2_build_memory          = '3.GB'
+outdir                              = 'results'
 
 aws.client.anonymous = true // fixes S3 access issues on self-hosted runners