2 files changed, 45 insertions, 2 deletions
diff --git a/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-01.js b/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-01.js
index 6fd8fb8150..00582bbe1d 100644
--- a/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-01.js
+++ b/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-01.js
@@ -20,6 +20,11 @@
  * code by having a tag called "padding" and a property
  * value called "margin".
  */
+
+const { PrefObserver } = require("devtools/client/shared/prefs");
+const PREF_ENABLE_MDN_DOCS_TOOLTIP =
+  "devtools.inspector.mdnDocsTooltip.enabled";
+
 const TEST_URI = `
   <html>
     <head>
@@ -35,13 +40,51 @@ const TEST_URI = `
 `;
 
 add_task(function* () {
+  info("Ensure the pref is true to begin with");
+  let initial = Services.prefs.getBoolPref(PREF_ENABLE_MDN_DOCS_TOOLTIP);
+  if (initial != true) {
+    yield setBooleanPref(PREF_ENABLE_MDN_DOCS_TOOLTIP, true);
+  }
+
   yield addTab("data:text/html;charset=utf8," + encodeURIComponent(TEST_URI));
   let {inspector, view} = yield openRuleView();
   yield selectNode("padding", inspector);
   yield testMdnContextMenuItemVisibility(view);
+
+  info("Ensure the pref is reset to its initial value");
+  let eventual = Services.prefs.getBoolPref(PREF_ENABLE_MDN_DOCS_TOOLTIP);
+  if (eventual != initial) {
+    yield setBooleanPref(PREF_ENABLE_MDN_DOCS_TOOLTIP, initial);
+  }
 });
 
 /**
+ * Set a boolean pref, and wait for the pref observer to
+ * trigger, so that code listening for the pref change
+ * has had a chance to update itself.
+ *
+ * @param pref {string} Name of the pref to change
+ * @param state {boolean} Desired value of the pref.
+ *
+ * Note that if the pref already has the value in `state`,
+ * then the prefObserver will not trigger. So you should only
+ * call this function if you know the pref's current value is
+ * not `state`.
+ */
+function* setBooleanPref(pref, state) {
+  let oncePrefChanged = defer();
+  let prefObserver = new PrefObserver("devtools.");
+  prefObserver.on(pref, oncePrefChanged.resolve);
+
+  info("Set the pref " + pref + " to: " + state);
+  Services.prefs.setBoolPref(pref, state);
+
+  info("Wait for prefObserver to call back so the UI can update");
+  yield oncePrefChanged.promise;
+  prefObserver.off(pref, oncePrefChanged.resolve);
+}
+
+/**
  * Tests that the MDN context menu item is shown when it should be,
  * and hidden when it should be.
  *   - iterate through every node in the rule view
diff --git a/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-03.js b/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-03.js
index ac5f636a20..eb1527d7b9 100644
--- a/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-03.js
+++ b/devtools/client/inspector/rules/test/browser_rules_context-menu-show-mdn-docs-03.js
@@ -32,7 +32,7 @@ add_task(function* () {
   info("Ensure the pref is true to begin with");
   let initial = Services.prefs.getBoolPref(PREF_ENABLE_MDN_DOCS_TOOLTIP);
   if (initial != true) {
-    setBooleanPref(PREF_ENABLE_MDN_DOCS_TOOLTIP, true);
+    yield setBooleanPref(PREF_ENABLE_MDN_DOCS_TOOLTIP, true);
   }
 
   yield addTab("data:text/html;charset=utf8," + encodeURIComponent(TEST_DOC));
@@ -58,7 +58,7 @@ add_task(function* () {
   info("Ensure the pref is reset to its initial value");
   let eventual = Services.prefs.getBoolPref(PREF_ENABLE_MDN_DOCS_TOOLTIP);
   if (eventual != initial) {
-    setBooleanPref(PREF_ENABLE_MDN_DOCS_TOOLTIP, initial);
+    yield setBooleanPref(PREF_ENABLE_MDN_DOCS_TOOLTIP, initial);
   }
 });