add simple docs

docs/webui.md

@@ -295,3 +295,15 @@ Design draft preview:
 | Catalog  | _`View`_ ✔ / _`Create`_ ✔ / _`Edit`_ ✔ / _`Delete`_ ✔ |
 | Schema   | _`View`_ ✔ / _`Create`_ ✘ / _`Edit`_ ✘ / _`Delete`_ ✘ |
 | Table    | _`View`_ ✔ / _`Create`_ ✘ / _`Edit`_ ✘ / _`Delete`_ ✘ |
+
+## E2E test
+End-to-end testing for web frontends is conducted using the [Selenium](https://www.selenium.dev/documentation/) testing framework, which is Java-based.
+
+Test cases can be found in the project directory: `integration-test/src/test/java/com/datastrato/gravitino/integration/test/web/ui`, where the `pages` directory is designated for storing definitions of frontend elements, among others.
+The root directory contains the actual steps for the test cases.
+
+:::tip
+ While writing test cases, running them in a local environment may not pose any issues. However, due to the limited performance capabilities of GitHub Actions, scenarios involving delayed DOM loading—such as the time taken for a popup animation to open—can result in test failures.
+
+ To circumvent this issue, it is necessary to manually insert a delay operation, for instance, by adding such as `Thread.sleep(sleepTimeMillis)`. This ensures that the test waits for the completion of the delay animation before proceeding with the next operation, thereby avoiding the problem.
+:::

integration-test/src/test/java/com/datastrato/gravitino/integration/test/web/ui/pages/MetalakePage.java

@@ -237,6 +237,8 @@ public boolean verifyShowMetalakeDetails(String name) {
 
   public boolean verifyEmptyMetalake() {
     try {
+      // To prevent errors in actions, it is necessary to wait for the completion of frontend delay
+      // animations before proceeding with the next step of operation verification.
       Thread.sleep(sleepTimeMillis);
       String xpath =
           "//div[@data-refer='metalake-table-grid']//div[contains(@class, 'MuiDataGrid-overlay')]";