diff --git a/src/converters/assimp.ts b/src/converters/assimp.ts
index cac4f9f..9db38ce 100644
--- a/src/converters/assimp.ts
+++ b/src/converters/assimp.ts
@@ -1,4 +1,10 @@
-import { execFile } from "node:child_process";
+import { execFile as execFileOriginal } from "node:child_process";
+
+type ExecFileFn = (
+  cmd: string,
+  args: string[],
+  callback: (err: Error | null, stdout: string, stderr: string) => void,
+) => void;
 
 export const properties = {
   from: {
@@ -116,8 +122,8 @@ export async function convert(
   fileType: string,
   convertTo: string,
   targetPath: string,
-  // eslint-disable-next-line @typescript-eslint/no-unused-vars
   options?: unknown,
+  execFile: ExecFileFn = execFileOriginal,
 ): Promise<string> {
   return new Promise((resolve, reject) => {
     execFile("assimp", ["export", filePath, targetPath], (error, stdout, stderr) => {
diff --git a/tests/assimp.test.ts b/tests/assimp.test.ts
new file mode 100644
index 0000000..062c115
--- /dev/null
+++ b/tests/assimp.test.ts
@@ -0,0 +1,70 @@
+import type { ExecFileException } from "node:child_process";
+import { expect, test } from "bun:test";
+import { convert } from "../src/converters/assimp";
+
+type ExecFileFn = (
+  cmd: string,
+  args: string[],
+  callback: (err: Error | null, stdout: string, stderr: string) => void,
+) => void;
+
+test("convert resolves when execFile succeeds", async () => {
+  const originalConsoleLog = console.log;
+
+  let loggedMessage = "";
+  console.log = (msg) => {
+    loggedMessage = msg;
+  };
+
+  const mockExecFile: ExecFileFn = (
+    _cmd: string,
+    _args: string[],
+    callback: (err: ExecFileException | null, stdout: string, stderr: string) => void,
+  ) => {
+    callback(null, "Fake stdout", "");
+  };
+
+  const result = await convert("input.obj", "obj", "stl", "output.stl", undefined, mockExecFile);
+
+  console.log = originalConsoleLog;
+
+  expect(result).toBe("Done");
+  expect(loggedMessage).toBe("stdout: Fake stdout");
+});
+
+test("convert rejects when execFile fails", async () => {
+  const mockExecFile: ExecFileFn = (
+    _cmd: string,
+    _args: string[],
+    callback: (err: ExecFileException | null, stdout: string, stderr: string) => void,
+  ) => {
+    callback(new Error("Test error"), "", "");
+  };
+
+  expect(convert("input.obj", "obj", "stl", "output.stl", undefined, mockExecFile)).rejects.toMatch(
+    /error: Error: Test error/,
+  );
+});
+
+test("convert logs stderr when present", async () => {
+  const originalConsoleError = console.error;
+
+  let loggedMessage = "";
+  console.error = (msg) => {
+    loggedMessage = msg;
+  };
+
+  const mockExecFile = (
+    _cmd: string,
+    _args: string[],
+    cb: (err: Error | null, stdout: string, stderr: string) => void,
+  ) => {
+    cb(null, "", "Fake stderr");
+  };
+
+  await convert("file.obj", "obj", "stl", "out.stl", undefined, mockExecFile);
+
+  console.error = originalConsoleError;
+
+  expect(loggedMessage).toBe("stderr: Fake stderr");
+});