Updated canary bazel test to use a more appropriate 'guard` statement instead of 'if'.

PiperOrigin-RevId: 219196055
diff --git a/src/TulsiEndToEndTests/ButtonsEndToEndTest.swift b/src/TulsiEndToEndTests/ButtonsEndToEndTest.swift
index d226679..9bc498a 100644
--- a/src/TulsiEndToEndTests/ButtonsEndToEndTest.swift
+++ b/src/TulsiEndToEndTests/ButtonsEndToEndTest.swift
@@ -41,14 +41,17 @@
   }
 
   func testButtonsWithCanaryBazel() throws {
-    if let canaryBazelURL = fakeBazelWorkspace.canaryBazelURL {
-      XCTAssert(fileManager.fileExists(atPath: canaryBazelURL.path), "Bazel canary is missing.")
-      bazelURL = canaryBazelURL
-      let buttonsProjectPath = "src/TulsiEndToEndTests/Resources/Buttons.tulsiproj"
-      let xcodeProjectURL = generateXcodeProject(tulsiProject: buttonsProjectPath,
-                                                 config: "Buttons")
-      testXcodeProject(xcodeProjectURL, scheme: "ButtonsLogicTests")
+    guard let canaryBazelURL = fakeBazelWorkspace.canaryBazelURL else {
+      XCTFail("Expected Bazel canary URL.")
+      return
     }
+    XCTAssert(fileManager.fileExists(atPath: canaryBazelURL.path), "Bazel canary is missing.")
+
+    bazelURL = canaryBazelURL
+    let buttonsProjectPath = "src/TulsiEndToEndTests/Resources/Buttons.tulsiproj"
+    let xcodeProjectURL = generateXcodeProject(tulsiProject: buttonsProjectPath,
+                                               config: "Buttons")
+    testXcodeProject(xcodeProjectURL, scheme: "ButtonsLogicTests")
   }
 
   func testInvalidConfig() throws {