Add acceptance test for getting an empty list of groups of a user

tests/acceptance/features/apiProvisioning-v1/getUserGroups.feature

@@ -52,4 +52,12 @@ So that I can manage group membership
 		When user "anotheruser" sends HTTP method "GET" to API endpoint "/cloud/users/newuser/groups"
 		Then the OCS status code should be "997"
 		And the HTTP status code should be "401"
-		And the API should not return any data
+		And the API should not return any data
+
+	Scenario: admin gets groups of an user who is not in any groups
+		Given user "brand-new-user" has been created
+		And group "unused-group" has been created
+		When user "admin" sends HTTP method "GET" to API endpoint "/cloud/users/brand-new-user/groups"
+		Then the OCS status code should be "100"
+		And the HTTP status code should be "200"
+		And the list of groups returned by the API should be empty

tests/acceptance/features/bootstrap/Provisioning.php

@@ -1583,6 +1583,19 @@ public function theListOfUsersReturnedByTheApiShouldBeEmpty() {
 		);
 	}
 
+	/**
+	 * @Then /^the list of groups returned by the API should be empty$/
+	 *
+	 * @return void
+	 */
+	public function theListOfGroupsReturnedByTheApiShouldBeEmpty() {
+		$groupsList = $this->response->xml()->data[0]->groups[0];
+		PHPUnit_Framework_Assert::assertEmpty(
+			$groupsList,
+			"Groups list is not empty but it should be empty"
+		);
+	}
+
 	/**
 	 * @BeforeScenario
 	 * @AfterScenario