Add test for "go to first" feature

src/test/rustdoc-gui/search-result-go-to-first.goml

@@ -0,0 +1,20 @@
+// This test ensures that the "go_to_first" feature is working as expected.
+
+// First, we check that the first page doesn't have the string we're looking for to ensure
+// that the feature is changing page as expected.
+goto: file://|DOC_PATH|/test_docs/index.html
+assert-text-false: (".fqn .in-band", "Struct test_docs::Foo")
+
+// We now check that we land on the search result page if "go_to_first" isn't set.
+goto: file://|DOC_PATH|/test_docs/index.html?search=struct%3AFoo
+// Waiting for the search results to appear...
+wait-for: "#titles"
+assert-text-false: (".fqn .in-band", "Struct test_docs::Foo")
+// Ensure that the search results are displayed, not the "normal" content.
+assert-css: ("#main", {"display": "none"})
+
+// Now we can check that the feature is working as expected!
+goto: file://|DOC_PATH|/test_docs/index.html?search=struct%3AFoo&go_to_first=true
+// Waiting for the page to load...
+wait-for: 500
+assert-text: (".fqn .in-band", "Struct test_docs::Foo")