Add PhET widget code coverage (#1620)

## Summary:
Add new tests to ensure maximal code coverage of the PhET widget. This is based on the new code from the [a11y update, PR #1619](#1619) and should be merged in after the a11y update is merged in.
* Check that fullscreen button renders when the simulation loads successfully
* Check that fullscreen button does not render when the simulation fails to load
* Check that the locale warning banner renders when the `kaLocale` is not available for the requested PhET simulation

Issue: LEMS-2277

## Test plan:
* `yarn jest packages/perseus/src/widgets/phet-simulation/phet-simulation.test.ts`

Author: aemandine

Reviewers: SonicScrewdriver

Required Reviewers:

Approved By: SonicScrewdriver

Checks: ❌ codecov/project, ✅ codecov/patch, ✅ Upload Coverage (ubuntu-latest, 20.x), ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Jest Coverage (ubuntu-latest, 20.x), ✅ Check builds for changes in size (ubuntu-latest, 20.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ Cypress (ubuntu-latest, 20.x), ✅ Publish Storybook to Chromatic (ubuntu-latest, 20.x), ✅ gerald

Pull Request URL: #1620

.changeset/thick-eels-wait.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus": patch
+---
+
+Add code coverage

packages/perseus/src/widgets/phet-simulation/phet-simulation.test.ts

@@ -42,9 +42,15 @@ describe("phet-simulation widget", () => {
                 "https://phet.colorado.edu/sims/html/projectile-data-lab/latest/projectile-data-lab_all.html?locale=en",
             );
         });
+        // Fullscreen button should be available when the simulation renders successfully
+        await waitFor(() => {
+            expect(
+                screen.getByRole("button", {name: "Fullscreen"}),
+            ).toBeInTheDocument();
+        });
     });
 
-    it("should display an error for a non-PhET URL", async () => {
+    it("should display an error and hide fullscreen button for a non-PhET URL", async () => {
         // Arrange
         const apiOptions: APIOptions = {
             isMobile: false,
@@ -57,7 +63,48 @@ describe("phet-simulation widget", () => {
         await waitFor(() => {
             expect(
                 screen.getByText("Sorry, this simulation cannot load."),
-            ).toBeDefined();
+            ).toBeInTheDocument();
+        });
+        // Fullscreen button should not be in the document when the simulation cannot load
+        await waitFor(() => {
+            expect(
+                screen.queryByRole("button", {name: "Fullscreen"}),
+            ).not.toBeInTheDocument();
+        });
+    });
+
+    it("should display a locale warning for unavailable locale for PhET", async () => {
+        // Arrange
+        const apiOptions: APIOptions = {
+            isMobile: false,
+        };
+        jest.spyOn(Dependencies, "getDependencies").mockReturnValue({
+            ...testDependencies,
+            kaLocale: "zz",
+        });
+
+        // Act
+        renderQuestion(question1, apiOptions);
+
+        // Assert
+        await waitFor(() => {
+            expect(
+                screen.getByText(
+                    "Sorry, this simulation isn't available in your language.",
+                ),
+            ).toBeInTheDocument();
+        });
+        await waitFor(() => {
+            expect(screen.queryByTitle("Projectile Data Lab")).toHaveAttribute(
+                "src",
+                "https://phet.colorado.edu/sims/html/projectile-data-lab/latest/projectile-data-lab_all.html?locale=zz",
+            );
+        });
+        // Fullscreen button should be available when the simulation renders successfully
+        await waitFor(() => {
+            expect(
+                screen.getByRole("button", {name: "Fullscreen"}),
+            ).toBeInTheDocument();
         });
     });