Writing Tests for File Uploads

Testing file upload endpoints is crucial to ensure that your application can handle different file types, sizes, and potential errors. In this guide, we’ll demonstrate how to write effective tests for your file upload endpoints in FastAPI.

Testing Successful File Uploads

Python

def test_upload_file(client):
    file_path = "test.txt"
    with open(file_path, "rb") as f:
        files = {"file": (file_path, f, "text/plain")}
        response = client.post("/upload", files=files)

    assert response.status_code == 200
    assert "message" in response.json()
    assert response.json()["message"] == "File uploaded successfully"

Testing File Validation

Python

def test_upload_invalid_file_type(client):
    file_path = "test.jpg"
    with open(file_path, "rb") as f:
        files = {"file": (file_path, f, "image/jpeg")}
        response = client.post("/upload", files=files)

    assert response.status_code == 400
    assert "Invalid file type" in response.json()["detail"]

def test_upload_large_file(client):
    # Create a large file
    large_file_path = "large_file.txt"
    with open(large_file_path, "w") as f:
        f.write("This is a very large file")

    with open(large_file_path, "rb") as f:
        files = {"file": (large_file_path, f, "text/plain")}
        response = client.post("/upload", files=files)

    assert response.status_code == 400
    assert "File size exceeds maximum limit" in response.json()["detail"]

Testing Error Handling

Python

def test_upload_no_file(client):
    response = client.post("/upload")

    assert response.status_code == 422
    assert "field required" in response.json()["detail"]

Additional Factors

• File Storage: If you’re storing uploaded files, test that they are stored correctly and can be retrieved.
• Security: Test for vulnerabilities like file upload attacks and ensure proper validation of uploaded files.
• Performance: Test the file upload endpoint under load to ensure it can handle large files and concurrent uploads.

By writing comprehensive tests for your file upload endpoints, you can ensure that your application can handle different file types, sizes, and potential errors, providing a robust and reliable user experience.