diff --git a/src/swc/__tests__/dirWorker.test.ts b/src/swc/__tests__/dirWorker.test.ts
new file mode 100644
index 0000000..0644d6e
--- /dev/null
+++ b/src/swc/__tests__/dirWorker.test.ts
@@ -0,0 +1,82 @@
+import { Options } from "@swc/core";
+import handleCompile from "../dirWorker";
+import { CliOptions, DEFAULT_OUT_FILE_EXTENSION } from "../options";
+import * as utilModule from '../util';
+
+type HandleCompileOptions = {
+  cliOptions: CliOptions;
+  swcOptions: Options;
+  sync: false,
+  outDir: "outDir",
+  filename: string,
+  outFileExtension?: string;
+}
+
+const createHandleCompileOptions = (options?: Partial<HandleCompileOptions>): HandleCompileOptions => ({
+  cliOptions: {
+    outDir: "",
+    outFile: "",
+    filename: "",
+    stripLeadingPaths: false,
+    filenames: [],
+    sync: false,
+    workers: undefined,
+    sourceMapTarget: undefined,
+    extensions: [],
+    watch: false,
+    copyFiles: false,
+    outFileExtension: "",
+    includeDotfiles: false,
+    deleteDirOnStart: false,
+    quiet: true,
+    only: [],
+    ignore: [],
+  },
+  swcOptions: {},
+  sync: false,
+  outDir: "outDir",
+  filename: "",
+  ...options,
+});
+
+jest.mock('../util', () => ({
+  ...jest.requireActual("../util"),
+  compile: jest.fn(),
+}));
+
+describe("dirWorker", () => {
+  it('should call "compile" with the "DEFAULT_OUT_FILE_EXTENSION" when "outFileExtension" is undefined', async () => {
+    const filename = 'test';
+    const options = createHandleCompileOptions({
+      filename: `${filename}.ts`
+    });
+
+    try {
+      await handleCompile(options);
+    } catch (err) {
+      // We don't care about the error in this test, we want to make sure that "compile" was called
+    }
+
+    // Assert that subFunction was called with the correct parameter
+    expect(utilModule.compile).toHaveBeenCalledWith(options.filename, { sourceFileName: `../${options.filename}`}, options.sync, `${options.outDir}/${filename}.${DEFAULT_OUT_FILE_EXTENSION}`);
+  });
+});
+
+describe("dirWorker", () => {
+  it('should call "compile" with "outFileExtension" when undefined', async () => {
+    const filename = 'test';
+    const options = createHandleCompileOptions({
+      filename: `${filename}.ts`,
+      outFileExtension: 'cjs'
+    });
+
+    try {
+      await handleCompile(options);
+    } catch (err) {
+      // We don't care about the error in this test, we want to make sure that "compile" was called
+    }
+
+    // Assert that subFunction was called with the correct parameter
+    expect(utilModule.compile).toHaveBeenCalledWith(options.filename, { sourceFileName: `../${options.filename}`}, options.sync, `${options.outDir}/${filename}.${options.outFileExtension}`);
+  });
+});