Travis CI: Verify that Ansible check mode passes

For sake of CI speed, the check mode is verified only against one
container (the latest version of each operating system platform).
Such check is performed before, and after, the Ansible role has been
applied to the managed instance.

.travis.yml

@@ -37,8 +37,10 @@ install:
 
 script:
   - cd tests
-  - docker-compose config --services | grep $PLATFORM | xargs docker-compose up -d
-  - ansible-playbook $PLAYBOOK -l $PLATFORM
+  - docker-compose config --services | grep "$PLATFORM" | xargs docker-compose up -d
+  - ansible-playbook $PLAYBOOK -l "$PLATFORM:&latest" --check --diff
+  - ansible-playbook $PLAYBOOK -l "$PLATFORM" -vv
+  - ansible-playbook $PLAYBOOK -l "$PLATFORM:&latest" --check --diff
 
 before_cache:
   # Put docker images used during this run into travis cache (if not already cached).

tests/inventory

@@ -13,3 +13,8 @@ tests_ubuntu14_1 ansible_connection=docker
 tests_ubuntu16_1 ansible_connection=docker
 tests_ubuntu18_1 ansible_connection=docker
 tests_ubuntu20_1 ansible_connection=docker
+
+[latest]
+tests_centos8_1
+tests_debian10_1
+tests_ubuntu20_1

tests/root.yml

@@ -20,4 +20,5 @@
     rvm1_install_path: '/opt/rvm'
   tasks:
     - import_tasks: assertions.yml
+      when: not ansible_check_mode
   tags: validate

tests/user.yml

@@ -22,4 +22,5 @@
     rvm1_install_path: '/home/user/.rvm'
   tasks:
     - import_tasks: assertions.yml
+      when: not ansible_check_mode
   tags: validate