Add the ability to specify an install_dir to the gem module (#38195)

* Add the ability to specify an install_dir to the gem module

* Add GEM_HOME when installing a non-global gem

* Add tests for custom gem path

* Fix sanity tests

* Add changelog entry

* Rebase and add tests for incorrect options

Co-authored by: Antoine Catton <devel@antoine.catton.fr>

test/units/modules/packaging/language/test_gem.py

@@ -0,0 +1,121 @@
+# Copyright (c) 2018 Antoine Catton
+# MIT License (see licenses/MIT-license.txt or https://opensource.org/licenses/MIT)
+import copy
+import json
+
+import pytest
+
+from ansible.modules.packaging.language import gem
+from units.modules.utils import AnsibleExitJson, AnsibleFailJson, ModuleTestCase, set_module_args
+
+
+def get_command(run_command):
+    """Generate the command line string from the patched run_command"""
+    args = run_command.call_args[0]
+    command = args[0]
+    return ' '.join(command)
+
+
+class TestGem(ModuleTestCase):
+    def setUp(self):
+        super(TestGem, self).setUp()
+        self.rubygems_path = ['/usr/bin/gem']
+        self.mocker.patch(
+            'ansible.modules.packaging.language.gem.get_rubygems_path',
+            lambda module: copy.deepcopy(self.rubygems_path),
+        )
+
+    @pytest.fixture(autouse=True)
+    def _mocker(self, mocker):
+        self.mocker = mocker
+
+    def patch_installed_versions(self, versions):
+        """Mocks the versions of the installed package"""
+
+        target = 'ansible.modules.packaging.language.gem.get_installed_versions'
+
+        def new(module, remote=False):
+            return versions
+
+        return self.mocker.patch(target, new)
+
+    def patch_rubygems_version(self, version=None):
+        target = 'ansible.modules.packaging.language.gem.get_rubygems_version'
+
+        def new(module):
+            return version
+
+        return self.mocker.patch(target, new)
+
+    def patch_run_command(self):
+        target = 'ansible.module_utils.basic.AnsibleModule.run_command'
+        return self.mocker.patch(target)
+
+    def test_fails_when_user_install_and_install_dir_are_combined(self):
+        set_module_args({
+            'name': 'dummy',
+            'user_install': True,
+            'install_dir': '/opt/dummy',
+        })
+
+        with pytest.raises(AnsibleFailJson) as exc:
+            gem.main()
+
+        result = exc.value.args[0]
+        assert result['failed']
+        assert result['msg'] == "install_dir requires user_install=false"
+
+    def test_passes_install_dir_to_gem(self):
+        # XXX: This test is extremely fragile, and makes assuptions about the module code, and how
+        #      functions are run.
+        #      If you start modifying the code of the module, you might need to modify what this
+        #      test mocks. The only thing that matters is the assertion that this 'gem install' is
+        #      invoked with '--install-dir'.
+
+        set_module_args({
+            'name': 'dummy',
+            'user_install': False,
+            'install_dir': '/opt/dummy',
+        })
+
+        self.patch_rubygems_version()
+        self.patch_installed_versions([])
+        run_command = self.patch_run_command()
+
+        with pytest.raises(AnsibleExitJson) as exc:
+            gem.main()
+
+        result = exc.value.args[0]
+        assert result['changed']
+        assert run_command.called
+
+        assert '--install-dir /opt/dummy' in get_command(run_command)
+
+    def test_passes_install_dir_and_gem_home_when_uninstall_gem(self):
+        # XXX: This test is also extremely fragile because of mocking.
+        #      If this breaks, the only that matters is to check whether '--install-dir' is
+        #      in the run command, and that GEM_HOME is passed to the command.
+        set_module_args({
+            'name': 'dummy',
+            'user_install': False,
+            'install_dir': '/opt/dummy',
+            'state': 'absent',
+        })
+
+        self.patch_rubygems_version()
+        self.patch_installed_versions(['1.0.0'])
+
+        run_command = self.patch_run_command()
+
+        with pytest.raises(AnsibleExitJson) as exc:
+            gem.main()
+
+        result = exc.value.args[0]
+
+        assert result['changed']
+        assert run_command.called
+
+        assert '--install-dir /opt/dummy' in get_command(run_command)
+
+        update_environ = run_command.call_args[1].get('environ_update', {})
+        assert update_environ.get('GEM_HOME') == '/opt/dummy'