Testing Java methods
Method-level testing exercises the different conditions defined in the method code in isolation from other methods, allowing you to test each individual method independently. The focus is generally to ensure that the method correctly processes all of its possible inputs. You can use the method-level test pattern that is provided for this purpose. Method-level testing is often a required first step toward class-level testing.
To test a Java method:
- Create a test for a method.
If the code has not been written and you want to follow a test-first design approach, at minimum define the method signature before generating the test.
- Use the test data table to define simple values for method parameters.
All method parameters and the return value of the method are automatically identified as inputs or expected outputs in the test data table. Environmental parameters such as global variables or attributes of the class can also be considered input or output parameters, but they do not appear automatically in the test data table. To test these variables and attributes, you can add initialization points before the call to the method-under-test and add validation actions after the call to the method-under-test.
- Make sure that the component containing the method-under-test is in the right state for the test.
If you need to invoke methods to put your component-under-test in a particular state before you invoke the method that you are testing, you can add method calls to the test behavior script.
For example, you might want to test how the pop() method works on a stack (that is, remove an item from the top of the stack). However, to be able to remove something, first add something to the stack. Therefore, you often need to invoke some methods to meet the pre-conditions prior to calling the method-under-test.
- Run the test.
Run the test to make sure that everything is working properly. If failures are reported, use the Test Data Comparator to help you understand the test results. If you still do not understand the results, use the debugger. Keep rerunning the test until it passes.
- Define several data sets using data partitioning techniques.
After you define a test with simple parameter values, it's important to enhance the test with more data in the domain of possible values. An effective way to define test values is to perform data partitioning on all of the parameters that you have identified. Based on this data partitioning, use the test data table to create as many data sets as you think are necessary.
Also, you can increase your test coverage by including sets and ranges of values. However, realize that each value defined in a data set is seen as an individual test, and by increasing the number of individual tests, you also increase test execution time.
- Rerun the test.
It is possible that there are still differences between the expected values that you defined and the actual values that you observed. This may be the result of inappropriate inputs, inappropriate outputs, or a defect in the component-under-test. To troubleshoot, use the debugger and the Test Explorer view.
- Assess your test coverage.
To assess your test coverage, go to the Coverage view in the Profiling perspective and profile the test that you just defined. If less than 100% of your lines are covered, try expanding the range of data you are covering, adding some new data sets, or defining a new test. Details about monitoring code coverage can be found in the online Help.
To decide what data sets to add, identify the lines of code that are not covered. Usually those lines are related to decisions in your code, such as if statements. Very often, because the condition is always evaluated to false, the block of code following the decision is not covered. To cover this block of code, identify the right parameter values and add a data set with these values.
For an extended example that describes how to test a method, see Defining test data.
Related concepts
Test strategies
Java subsystems
State-based testing techniques
Related tasks
Testing Java classes