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Step Five: Write Selected Test Cases

Now it is time for the main event: actually writing the test case steps and specifying test data. This is a task that you can expect to take ten to forty-five minutes for each test case. That might work out to approximately ten test cases in a typical work day. So, you must be selective to get the most value in return for your limited available time.

Focus on the test cases that seem most in need of additional detail. For example, select system test cases that cover:

• High priority use cases or features
• Software components that are currently available for testing (rather than specifying tests on components that cannot actually be tested yet)
• Features that must work properly before other features can be exercised (e.g., if login does not work, you cannot test anything that requires a logged in user)
• Features that are needed for product demos or screenshots
• Requirements that need to be made more clear

Each test case should be simple enough to clearly succeed or fail, with little or no gray area in between. Ideally, the steps of a test case are a simple sequence: set up the test situation, exercise the system with specific test inputs, verify the correctness of the system outputs. You may use programming constructs such as if-statements or loops, if needed.

Systems that are highly testable tend to have a large number of simple test cases that follow the set-up-exercise-verify pattern. For those test cases, a one-column format can clearly express the needed steps. However, not all test cases are so simple. Sometimes it is impractical to test one requirement at a time. Instead, some system test cases may be longer scenarios that exercise several requirements and verify correctness at each step. For those test cases, a two-column format can prove useful.

In the one-column format, each step is a brief verb phrase that describes the action that the tester should take. For example, "enter username," "enter password," "click 'Login'," "see Welcome page," and "verify that greeting has correct username" are all steps. Verification of expected outputs are written using the verbs "see" and "verify." If multiple inputs are needed, or multiple outputs must be verified, one-column test cases will simply have more steps.

In the two-column format, each test case step has two parts: a test input, and an expected output:

Test Input

The Test Input is a verb phrase describing what the tester should do in that step.

Expected Output

The Expected Output is a noun phrase describing all the output that the tester should observe at that step.

You may notice that the two formats for test cases mirror the two formats for use cases. The difference is that use cases are a form of requirements, whereas test cases deal with more details of the implemented system. Use cases focus mainly on the user's tasks and how the system supports those tasks, while specifying as few implementation details as possible. A major advantage of use cases is that they are simple enough to be read by actual users who can help validate requirements. In contrast, test cases should more technical documents with enough implementation detail to allow any member of the development team to carry out a test exactly the same way.

If you have written use cases, they can be copied and pasted as a good starting point for test cases. When leveraging use cases in this way, make sure to add enough detail to make the test reliably repeatable.

If you only have one test input value for a given test case, then you could write that test data value directly into the step where it is used. However, many test cases will have a set of test data values which must all be used to adequately cover all possible inputs. We encourage you to define and use test input variables. Each variable is defined with a set of its selected values, and then it is used in test case steps just as you would use a variable in a programming language. When carrying out the tests, the tester should repeat each test case with each possible combination of test variable values, or as many as practical.

Carefully selecting test data is as important as defining the steps of the test case. The concepts of boundary conditions and equivalence partitions are key to good test data selection. Try these steps to select test data:

• Determine the set of all input values that can possibly be entered for a given input parameter. For example, the age of a person might be entered as any integer.
• Define the boundary between valid and invalid input values. For example, negative ages are nonsense. You might also check for clearly unreasonable inputs. For example, an age entered as 200 is much more likely to be a typo than a user who is actually two-hundred years old.
• Review the requirements and find boundaries in the valid range that should cause the system to behave in different ways. For example, the system might treat minors differently than adults, so the boundary would be age 18.
• Now you have a set of equivalence partitions: sets of values that the system should treat uniformly. For example, all minors are treated one way, and all adults are treated another way. Double check the requirements to make sure that you have not missed a partition division, e.g., not all adults are old enough to drink alcohol in the U.S.
• Choose one input value somewhere in the middle of each equivalence partition (e.g., -5, 12, and 44), one directly on each boundary (e.g., 0 and 18), and one on each side of each boundary (e.g., 1, 17, and 19). Test data vales that are expected to cause errors (e.g., -5) should be tested in separate robustness test cases.
• In functional correctness test cases, make sure that you have inputs that will force the system to generate each possible type of response to valid input. And, in robustness test cases, make sure to force the system to generate each relevant error message.

Recall that one of the advantages of writing test cases is that it forces you to clearly think through the requirements. Capture your insights by writing notes and questions as you go. If a test case step exposes an unclear requirement, make a note of it in the appropriate part of the system requirements specification.

How ReadySET Pro Helps

ReadySET Pro contains several high-quality, reusable sample test cases. These test cases demonstrate the proper use of both formats, for both functional and robustness testing. You can preview the Test Case Template or any other template through the Document Map.

A separate "test case format" document defines a notation for expressing test case steps using a small set of standard keywords.

Each test case template in ReadySET Pro also indicates its preconditions. The preconditions of a test case describe conditions that must be true before the test can be carried out. Writing preconditions helps to avoid writing redundant steps for setting up the needed testing situation.

Step Six: Evaluate Test Cases

A suite of system test cases can find many defects, but still leave many other critical defects undetected. One clear way to guard against undetected defects is to increase the coverage of your test suite.

While a suite of unit tests might be evaluated in terms of its implementation coverage, a suite of system test cases should instead be evaluated in terms of specification coverage. Implementation coverage measures the percentage of lines of code that are executed by the unit test cases. If there is a line of code that is never executed, then there could be an undetected defect on that line. Specification coverage measures the percentage of written requirements that the system test suite covers. If there is a requirement that is not tested by any system test case, then you are not assured that the requirement has been satisfied.

You can evaluate the coverage of your system tests on two levels. First, the test suite itself is an organized table of contents for the test cases that can make it easy to notice parts of the system that are not being tested. Second, within an individual test case, the set of possible input values should cover all input value equivalence partitions for each parameter.

How ReadySET Pro Helps

ReadySET Pro's system test suite template and test case templates contain high-quality, reusable sample text that helps you plan and write test cases that cover all requirements. The templates encourage you to use a format that makes it easier to evaluate your software testing plans.

The light-weight, web-based nature of ReadySET Pro makes it easy for the entire development team to use and update the latest revisions of the system test suite. And, the comprehensive set of templates provided by ReadySET Pro helps you keep the system test documents in sync with the overall QA plan, the system requirements specification, and design documents.

Conclusion

This white paper laid out the steps needed to quickly create a system test suite and test cases using the ReadySET Pro templates. The keys to effectively system testing are to:

• Set explicit quality goals that are appropriate for the current release and understand where your test plan fits in your overall QA plan.
• Take a breadth-first approach by first mapping out a test suite with good coverage, and then prioritizing your work on specifying the test cases themselves.
• Write system test cases in enough detail that any member of the development team could carry out the testing to see the same results, and choose test input values that cover all equivalence partitions.
• Evaluate the system test suite and test cases to improve coverage of the system requirements.

ReadySET Pro provides valuable help for planning your system testing by giving you templates that include reusable content and set good examples for you to follow. Both of these advantages give you a big head start on your own test plans. ReadySET Pro users typically save at least three hours by using the test case suite and test case templates alone. See how these savings, and the savings from other templates, add up to days or weeks of project time by trying the ROI Calculator.

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