Bug 1877193 part 17 - Add a jit-test. r=mgaudet

Differential Revision: https://phabricator.services.mozilla.com/D200008

js/src/jit-test/tests/basic/shell-prefs.js

@@ -0,0 +1,24 @@
+// |jit-test| --setpref=site_based_pretenuring=false; --setpref=tests.uint32-pref=123450
+
+let names = getAllPrefNames();
+assertEq(names.length > 0, true, "Expected at least one pref!");
+assertEq(new Set(names).size, names.length, "Unexpected duplicate pref name");
+
+for (let name of names) {
+    let val = getPrefValue(name);
+    assertEq(typeof val === "number" || typeof val === "boolean", true);
+}
+
+// Check that --setpref worked. Note: this is just an arbitrary pref. If we ever
+// remove it, change this test to check a different one.
+assertEq(getPrefValue("site_based_pretenuring"), false);
+assertEq(getPrefValue("tests.uint32-pref"), 123450);
+
+// Must throw an exception for unknown pref names.
+let ex;
+try {
+    getPrefValue("some.invalid.pref");
+} catch (e) {
+    ex = e;
+}
+assertEq(ex.toString(), "Error: invalid pref name");

modules/libpref/init/StaticPrefList.yaml

@@ -7414,6 +7414,13 @@
   value: true
   mirror: always
 
+# No-op pref for testing the SpiderMonkey pref system.
+- name: javascript.options.tests.uint32-pref
+  type: uint32_t
+  value: 1
+  mirror: always
+  set_spidermonkey_pref: always
+
 # Enable fuse based destructuring
 - name: javascript.options.destructuring_fuse
   type: bool