nixos/tests/lxd-ui: add a basic selenium test to check the UI is functioning

nixos/tests/lxd/ui.nix

@@ -11,9 +11,37 @@ import ../make-test-python.nix ({ pkgs, lib, ... }: {
       lxd.ui.enable = true;
     };
 
-    environment.systemPackages = [ pkgs.curl ];
+    environment.systemPackages =
+      let
+        seleniumScript = pkgs.writers.writePython3Bin "selenium-script"
+          {
+            libraries = with pkgs.python3Packages; [ selenium ];
+          } ''
+          from selenium import webdriver
+          from selenium.webdriver.common.by import By
+          from selenium.webdriver.firefox.options import Options
+          from selenium.webdriver.support.ui import WebDriverWait
+
+          options = Options()
+          options.add_argument("--headless")
+          service = webdriver.FirefoxService(executable_path="${lib.getExe pkgs.geckodriver}")  # noqa: E501
+
+          driver = webdriver.Firefox(options=options, service=service)
+          driver.implicitly_wait(10)
+          driver.get("https://localhost:8443/ui")
+
+          wait = WebDriverWait(driver, 60)
+
+          assert len(driver.find_elements(By.CLASS_NAME, "l-application")) > 0
+          assert len(driver.find_elements(By.CLASS_NAME, "l-navigation__drawer")) > 0
+
+          driver.close()
+        '';
+      in
+      with pkgs; [ curl firefox-unwrapped geckodriver seleniumScript ];
   };
 
+
   testScript = ''
     machine.wait_for_unit("sockets.target")
     machine.wait_for_unit("lxd.service")
@@ -31,5 +59,8 @@ import ../make-test-python.nix ({ pkgs, lib, ... }: {
 
     # Ensure the endpoint returns an HTML page with 'LXD UI' in the title
     machine.succeed("curl -kLs https://localhost:8443/ui | grep '<title>LXD UI</title>'")
+
+    # Ensure the application is actually rendered by the Javascript
+    machine.succeed("PYTHONUNBUFFERED=1 selenium-script")
   '';
 })