Gradle Kotlin test fails due to NoClassDefFoundError

Hello. I’m trying to make a build & test pipeline for a Gradle project written in Kotlin using Spek Framework, but I get java.lang.NoClassDefFoundError on Spek tests which are based on Kotlin singleton objects (I think this might be the issue). The tests complete on my local machine and in my local Docker environment using both java and gradle images.

My CI script is as follows:

image: gradle:5.6.2

variables:
  GRADLE_OPTS: "-Dorg.gradle.daemon=false"

before_script:
  - export GRADLE_USER_HOME=`pwd`/.gradle

build:
  stage: build
  script: gradle --build-cache assemble
  cache:
    key: "$CI_COMMIT_REF_NAME"
    policy: push
    paths:
      - build
      - .gradle

test:
  stage: test
  script: gradle check --info
  cache:
    key: "$CI_COMMIT_REF_NAME"
    policy: push
    paths:
      - build
      - .gradle
  artifacts:
    reports:
      junit: build/test-results/test/TEST-*.xml

And the gradle test task output with --info flag:

link

same here.
i’m using a kotlin singleton object (called TestEnvironment) in my setup. on my local mashine everything works but on gitlab-ci im getting

java.lang.NoClassDefFoundError: Could not initialize class config.docker.TestEnvironment
    at tests.SetupPageIT.can access setup application(SetupPageIT.kt:18)