community.general/test/integration/test_environment.yml

- hosts: testhost
  vars:
    - test1:
        key1: val1
  roles:
    - { role: prepare_tests }
  tasks:
    - name: check that envvar does not exist
      shell: echo $key1
      register: test_env

    - assert:
        that:
            - '"val1" not in test_env.stdout'

    - name: check that envvar does exist
      shell: echo $key1
      environment: "{{test1}}"
      register: test_env2

    - assert:
        that:
            - '"val1" in test_env2.stdout'

- hosts: testhost
  tasks:
  vars:
    - test1:
        key1: val1
    - test2:
        key1: not1
        other1: val2
  environment: "{{test1}}"
  tasks:
    - name: check that play envvar does exist
      shell: echo $key1
      register: test_env

    - assert:
        that:
            - '"val1" in test_env.stdout'

    - name: check that task envvar does exist
      shell: echo $key1; echo $other1
      register: test_env2
      environment: "{{test2}}"

    - assert:
        that:
            - '"val1" not in test_env2.stdout'
            - '"not1" in test_env2.stdout'
            - '"val2" in test_env2.stdout'