Add GUI tests for collapse/expand actions

src/test/rustdoc-gui/shortcuts.goml

@@ -11,3 +11,21 @@ press-key: "?"
 assert-css: ("#help-button .popover", {"display": "block"})
 press-key: "Escape"
 assert-css: ("#help-button .popover", {"display": "none"})
+// Checking doc collapse and expand.
+// It should be displaying a "-":
+assert-text: ("#toggle-all-docs", "[\u2212]")
+press-key: "-"
+wait-for-text: ("#toggle-all-docs", "[+]")
+assert-attribute: ("#toggle-all-docs", {"class": "will-expand"})
+// Pressing it again shouldn't do anything.
+press-key: "-"
+assert-text: ("#toggle-all-docs", "[+]")
+assert-attribute: ("#toggle-all-docs", {"class": "will-expand"})
+// Expanding now.
+press-key: "+"
+wait-for-text: ("#toggle-all-docs", "[\u2212]")
+assert-attribute: ("#toggle-all-docs", {"class": ""})
+// Pressing it again shouldn't do anything.
+press-key: "+"
+assert-text: ("#toggle-all-docs", "[\u2212]")
+assert-attribute: ("#toggle-all-docs", {"class": ""})