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Test Cases are built around a single assertion from the Acceptance Criteria. More often than not, this means that each sentence presenting a in the AC section represents single acceptance criterion, and will generate a single Test Case. This single statement of what is to be tested should be included at the beginning of a Test Case's description.
To ensure that all the requirements of a given Functional Specification document have been fulfilled, you may want to compare your Test Cases to the acceptance criteria to see if there are any statements which have not been turned into Test Cases. If not, you have complete coverage of the Functional Specification you are testing.
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