How would you test a file upload feature that accepts PDF documents up to 10 MB?

What the interviewer wants to hear

• Positive tests: valid PDF small and at exactly 10 MB, with progress and success message
• Boundary and negative tests: just over 10 MB, zero-byte file, wrong types, renamed files
• Security: content checked on the server, not only the extension; malicious files handled
• Edge cases: long or Arabic file names, slow network, cancel and retry, duplicate uploads
• Check the stored file can be downloaded and opened correctly

Model answer

I start with positive cases: a normal PDF, and one exactly 10 MB, checking the progress bar, success message and that the file downloads and opens unchanged. Then boundaries and negatives: a file just over 10 MB, a zero-byte file, a JPG, a DOCX and a file renamed from .exe to .pdf, which the server should reject by checking content, not just the extension. I also test a password-protected or corrupted PDF and check the error messages are clear. For edge cases I try long file names, spaces, Arabic characters and duplicates, plus a slow or dropped network, cancelling mid-upload and uploading several files at once. Finally I check limits are enforced on the server through the API, not only in the browser, and that one user cannot open another user's files.

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