He compares the role of the tester as the role of the doctor.
Testers as doctors need to have knowledge about possible defects(illness) in order to develop the defect hypothesis.
They use these hypothesis to:
Designing of test cases.
Designing of test procedures
Assemble test sets
Select the testing levels for appropriate testing.
Example:unit and integration testing.
Evaluating the results of the test.
"A successful testing approach will prove the hypothesis is true,that is,the hypothesized defect was present,the software can be repaired."
Requirements/ specifications defects.
Since many requirements and specification documents are written using a natural language representation.
Here,the defects may arise because the requirements and specifications are written in the local languages ,some people may not understand the document clearly.
These may arise ambiguous,contradictory,unclear ,imprecise and redundant requirements.