Add rustdoc-gui regression test for #137082

Author: GuillaumeGomez

tests/rustdoc-gui/code-example-buttons.goml

@@ -26,6 +26,8 @@ click: ".example-wrap .copy-button"
 move-cursor-to: ".search-input"
 assert-count: (".example-wrap:not(:hover) .button-holder.keep-visible", 0)
 assert-css: (".example-wrap .copy-button", { "visibility": "hidden" })
+// Since we clicked on the copy button, the clipboard content should have been updated.
+assert-clipboard: 'println!("nothing fancy");\nprintln!("but with two lines!");'
 
 define-function: (
     "check-buttons",

tests/rustdoc-gui/copy-path.goml

@@ -1,12 +1,17 @@
 // Checks that the "copy path" button is not triggering JS error and its display
-// isn't broken.
-go-to: "file://" + |DOC_PATH| + "/test_docs/fn.foo.html"
+// isn't broken and the copied path is as expected.
+go-to: "file://" + |DOC_PATH| + "/test_docs/foreign_impl_order/trait.Foo.html"
+
+// We ensure that the clipboard is empty.
+assert-clipboard: ""
 
 // First we store the size of the button before we click on it.
 store-size: ("#copy-path", {"width": width, "height": height})
 click: "#copy-path"
 // We wait for the new text to appear.
 wait-for: "#copy-path.clicked"
+// We check that the clipboard value is the expected one.
+assert-clipboard: "test_docs::foreign_impl_order::Foo"
 // We check that the size didn't change.
 assert-size: ("#copy-path.clicked", {"width": |width|, "height": |height|})
 // We wait for the button to turn back to its original state.