You must be a constructive schizophrenic. Be clear about the difference between your role as a programmer and as a tester. The tester in you must be suspicious, uncompromising, hostile, and compulsively obsessed with destroying, utterly destroying, the programmer's software. The tester in you is your Mr. Hyde - your Incredible Hulk. He must exercise what Gruenberger calls 'low cunning.'

Chapter 1, Section 2.3.

Software testing techniques by Boris Beizer

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