A test case is a collection of actions performed to ensure that a specific feature or operation of your software program is working properly. A Test Case is a set of test procedures, data, preconditions, and postconditions created for a specific test scenario in order to verify any requirement. The test case contains specified variables or conditions that a testing engineer might use to compare EXPECTED and actual outcomes in order to assess whether a software product meets the customer's needs.

Following are some good practices for writing test cases : 

• Simple and transparent test cases are required: Make your test cases as simple as possible. They must be clear and straightforward because the test case author may not be able to perform them. Use declarative language such as "go to the main page," "input data," "click here," and so on. This makes it easier to understand the test stages and speeds up the testing process.
• Create a test case that considers the end-user: Any software project's ultimate goal is to produce test cases that fulfil client requirements and are simple to use and run. A tester must write test cases from the standpoint of the end-user.
• Repetition of test cases should be avoided: Test instances should not be repeated. If a test case is required for the execution of another test case, use the test case id in the preconditioned column to refer to it.
• Make certain you have complete coverage: Make sure you write test cases to ensure you've COVERED all of the software requirements in the specification document. To verify that no functions or conditions are left untested, use the Traceability Matrix.
• Don't Make Assumptions: When creating a test case, don't make assumptions about the functioning and features of your software application. FOLLOW the specifications in the specification documents.
• Self-cleaning: The test case you write must RESTORE the Test Environment to its previous condition and should not render it unusable. This is particularly true when it comes to configuration testing.