adding test for trying to enable sync with invalid remote item id

tests/acceptance/features/apiSharingNg/enableDisableShareSync.feature

@@ -297,3 +297,40 @@ Feature:  enable or disable sync of incoming shares
       | resource      |
       | textfile0.txt |
       | FolderToShare |
+
+  @issue-8724
+  Scenario: try to enable share sync of a non-existent resource
+    When user "Brian" tries to enable share sync of a non-existent resource using the Graph API
+    Then the HTTP status code should be "400"
+    And the JSON data of the response should match
+      """
+      {
+        "type": "object",
+        "required": ["error"],
+        "properties": {
+          "error": {
+            "type": "object",
+            "required": [
+              "code",
+              "innererror",
+              "message"
+            ],
+            "properties": {
+              "code" : {
+                "const": "invalidRequest"
+              },
+              "innererror" : {
+                "type": "object",
+                "required": [
+                  "date",
+                  "request-id"
+                ]
+              },
+              "message" : {
+                "const": "mounting share failed"
+              }
+            }
+          }
+        }
+      }
+      """

tests/acceptance/features/bootstrap/SharingNgContext.php

@@ -714,6 +714,26 @@ class SharingNgContext implements Context {
 		$this->featureContext->setResponse($response);
 	}
 
+	/**
+	 * @When user :user tries to enable share sync of a non-existent resource using the Graph API
+	 *
+	 * @param string $user
+	 *
+	 * @return void
+	 */
+	public function userTriesToEnablsShareSyncOfNonExistentResourceUsingTheGraphApi(string $user):void {
+		$shareSpaceId = FeatureContext::SHARES_SPACE_ID;
+		$response =  GraphHelper::enableShareSync(
+			$this->featureContext->getBaseUrl(),
+			$this->featureContext->getStepLineRef(),
+			$this->featureContext->getActualUsername($user),
+			$this->featureContext->getPasswordForUser($user),
+			WebDavHelper::generateUUIDv4(),
+			$shareSpaceId
+		);
+		$this->featureContext->setResponse($response);
+	}
+
 	/**
 	 * @Then /^user "([^"]*)" should have sync (enabled|disabled) for share "([^"]*)"$/
 	 *