diff --git a/test/App.test.tsx b/test/App.test.tsx
index 0e9cf90..6b0c5b5 100644
--- a/test/App.test.tsx
+++ b/test/App.test.tsx
@@ -6,18 +6,21 @@ import { getMessage } from "./mocks/chrome.i18n";
 import { success, error, loading } from "./mocks/fetch";
 
 describe("App.tsx", () => {
+  const globalChrome = global.chrome;
+  const globalFetch = global.fetch;
+
   beforeEach(() => {
     const chrome: any = { i18n: { getMessage } };
     global.chrome = chrome;
   });
 
   afterEach(() => {
-    global.chrome = undefined;
+    global.chrome = globalChrome;
   });
 
   describe("when the request is loading", () => {
     beforeEach(() => { global.fetch = loading; });
-    afterEach(() => { global.fetch = undefined; });
+    afterEach(() => { global.fetch = globalFetch; });
 
     test("loading text is rendered", () => {
       render(<App/>);
@@ -27,7 +30,7 @@ describe("App.tsx", () => {
 
   describe("when the request is a success", () => {
     beforeEach(() => { global.fetch = success; });
-    afterEach(() => { global.fetch = undefined; });
+    afterEach(() => { global.fetch = globalFetch; });
 
     test("response is rendered", async () => {
       await act(() => render(<App/>));
@@ -37,7 +40,7 @@ describe("App.tsx", () => {
 
   describe("when the request throws an error", () => {
     beforeEach(() => { global.fetch = error; });
-    afterEach(() => { global.fetch = undefined; });
+    afterEach(() => { global.fetch = globalFetch; });
 
     test("error is rendered", async () => {
       await act(() => render(<App/>));
diff --git a/test/ErrorRenderer.test.tsx b/test/ErrorRenderer.test.tsx
index d530922..a2f7960 100644
--- a/test/ErrorRenderer.test.tsx
+++ b/test/ErrorRenderer.test.tsx
@@ -5,6 +5,7 @@ import { ErrorRenderer } from "~/components/ErrorRenderer";
 import { getMessage } from "./mocks/chrome.i18n";
 
 describe("ErrorRenderer.tsx", () => {
+  const globalChrome = global.chrome;
   const error = new Error("This is an example error message");
 
   beforeEach(() => {
@@ -14,7 +15,7 @@ describe("ErrorRenderer.tsx", () => {
   });
 
   afterEach(() => {
-    global.chrome = undefined;
+    global.chrome = globalChrome;
   });
 
   test("an error is rendered", () => {
diff --git a/test/ResponseRenderer.test.tsx b/test/ResponseRenderer.test.tsx
index ee75f07..3f3d2a8 100644
--- a/test/ResponseRenderer.test.tsx
+++ b/test/ResponseRenderer.test.tsx
@@ -5,13 +5,15 @@ import { ResponseRenderer } from "~/components/ResponseRenderer";
 import { getMessage } from "./mocks/chrome.i18n";
 
 describe("ResponseRenderer.tsx", () => {
+  const globalChrome = global.chrome;
+
   beforeEach(() => {
     const chrome: any = { i18n: { getMessage } };
     global.chrome = chrome;
   });
 
   afterEach(() => {
-    global.chrome = undefined;
+    global.chrome = globalChrome;
   });
 
   const defaultResponse = {
diff --git a/tsconfig.json b/tsconfig.json
index fe67d0c..6c289f7 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,14 +1,11 @@
 {
   "compilerOptions": {
     "strict": true,
-    "strictNullChecks": false,
     "module": "commonjs",
     "target": "ES2020",
-    "noImplicitAny": true,
     "moduleResolution": "node",
     "esModuleInterop": true,
     "jsx": "react",
-    "allowJs": true,
     "lib": [ "ES2020", "DOM" ],
     "baseUrl": "src/",
     "paths": { "~/*": ["js/*"] },