How to create a Test Coverage Matrix (TCM)?

As the name suggests Test Coverage Matrix is a table (matrix) that can be used to track the testing coverage for a feature or a module.

Why to use TCM?
TCM is a simple tool which can be used to ensure that all probable conditions / cases for a feature to be tested are thought of; and can help in identifying probable gaps. It acts like a checklist which ensures that the functionality of the given screen or unit is checked in all possible combinations (positive as well as negative, and special conditions).

How can I use TCM?
No complex tools are required; you can create a TCM on paper, notepad or Excel. A TCM has the following minimum columns:
 

Figure : Test Coverage Matrix - Simple Spreadsheet Structure


Advantages of TCM are that one can clearly visualize what all cases have been considered; and it also helps in identifying gaps in testing. Besides they make peer review of test coverage very easy to do.