diff --git a/.mocharc.js b/.mocharc.js
index 2d42f6515..896c1f327 100644
--- a/.mocharc.js
+++ b/.mocharc.js
@@ -2,5 +2,6 @@
 
 module.exports = {
     recursive: true,
+    extension: [".js", ".ts"],
     require: ["./test/setup", "./test/assert-ext", "./test/ts-node"],
 };
diff --git a/test/src/utils/typescript.ts b/test/src/utils/typescript.ts
index 576a4e682..282505ef8 100644
--- a/test/src/utils/typescript.ts
+++ b/test/src/utils/typescript.ts
@@ -1,11 +1,9 @@
 import proxyquire from "proxyquire";
 import sinon, { type SinonStub } from "sinon";
 import _ from "lodash";
-import * as process from "process";
 
 describe("utils/typescript", () => {
-    const processBackup = _.assign({}, process);
-    const processEnvBackup = _.assign({}, process.env);
+    const processEnvBackup = _.clone(process.env);
 
     let ts: typeof import("src/utils/typescript");
     let registerStub: SinonStub;
@@ -13,8 +11,7 @@ describe("utils/typescript", () => {
 
     beforeEach(() => {
         registerStub = sinon.stub();
-        ts = require("src/utils/typescript");
-        ts = proxyquire("src/utils/typescript", {
+        ts = proxyquire.noCallThru().load("src/utils/typescript", {
             "ts-node": {
                 register: registerStub,
                 REGISTER_INSTANCE,
@@ -24,7 +21,6 @@ describe("utils/typescript", () => {
 
     afterEach(() => {
         _.set(process, REGISTER_INSTANCE, undefined);
-        _.set(global, "process", processBackup);
         _.set(process, "env", processEnvBackup);
     });
 
@@ -53,7 +49,7 @@ describe("utils/typescript", () => {
         });
 
         it("should use swc if it is installed", () => {
-            ts = proxyquire("src/utils/typescript", {
+            ts = proxyquire.noCallThru().load("src/utils/typescript", {
                 "ts-node": {
                     register: registerStub,
                 },
@@ -71,7 +67,7 @@ describe("utils/typescript", () => {
         });
 
         it("should not use swc if not installed", () => {
-            ts = proxyquire("src/utils/typescript", {
+            ts = proxyquire.noCallThru().load("src/utils/typescript", {
                 "ts-node": {
                     register: registerStub,
                 },
@@ -83,13 +79,13 @@ describe("utils/typescript", () => {
             assert.calledOnceWith(
                 registerStub,
                 sinon.match({
-                    swc: undefined,
+                    swc: false,
                 }),
             );
         });
 
         it("should not throw if nothing is installed", () => {
-            ts = proxyquire("src/utils/typescript", {
+            ts = proxyquire.noCallThru().load("src/utils/typescript", {
                 "ts-node": null,
                 "@swc/core": null,
             });