[Styles] add unit tests (#3557)

* unit tests for inspector styles feature
* add mock capability for local storage

Co-authored-by: Deep Tailor <deep.j.tailor@nasa.gov>
Co-authored-by: Andrew Henry <akhenry@gmail.com>

src/utils/testing/mockLocalStorage.js

@@ -0,0 +1,33 @@
+export function mockLocalStorage() {
+    let store;
+
+    beforeEach(() => {
+        spyOn(Storage.prototype, 'getItem').and.callFake(getItem);
+        spyOn(Storage.prototype, 'setItem').and.callFake(setItem);
+        spyOn(Storage.prototype, 'removeItem').and.callFake(removeItem);
+        spyOn(Storage.prototype, 'clear').and.callFake(clear);
+
+        store = {};
+
+        function getItem(key) {
+            return store[key];
+        }
+
+        function setItem(key, value) {
+            store[key] = typeof value === 'string' ? value : JSON.stringify(value);
+        }
+
+        function removeItem(key) {
+            store[key] = undefined;
+            delete store[key];
+        }
+
+        function clear() {
+            store = {};
+        }
+    });
+
+    afterEach(() => {
+        store = undefined;
+    });
+}