What is Code Coverage?

Question

Hi there ,
I have 3 questions :

• What is CodeCoverage ?
• What is it good for ?
• What tools are used for analyzing Code Coverage ?

Answer 1

The term refers to how well your program is covered by your tests. See the following wikipedia article for more info:

http://en.wikipedia.org/wiki/Code_coverage

Answer 2

From wikipedia article

Code coverage is a measure used in software testing. It describes the degree to which the source code of a program has been tested. It is a form of testing that inspects the code directly and is therefore a form of white box testing[1]. Currently, the use of code coverage is extended to the field of digital hardware, the contemporary design methodology of which relies on Hardware description languages (HDLs).

Advocating the use of code coverage

A code coverage tool simply keeps track of which parts of your code get executed and which parts do not.

Usually, the results are granular down to the level of each line of code. So in a typical situation, you launch your application with a code coverage tool configured to monitor it. When you exit the application, the tool will produce a code coverage report which shows which lines of code were executed and which ones were not. If you count the total number of lines which were executed and divide by the total number of lines which could have been executed, you get a percentage. If you believe in code coverage, the higher the percentage, the better. In practice, reaching 100% is extremely rare.

The use of a code coverage tool is usually combined with the use of some kind of automated test suite. Without automated testing, a code coverage tool merely tells you which features a human user remembered to use. Such a tool is far more useful when it is measuring how complete your test suite is with respect to the code you have written.

Related articles

The Future of Code-Coverage Tools

The effectiveness of code coverage tools in software testing

Tools

Open Source Code Coverage Tools in Java

Answer 3

Code coverage is a measure used in software testing. It describes the degree to which the source code of a program has been tested.

http://en.wikipedia.org/wiki/Code_coverage

The wikipedia definition is pretty good, but in my own words code coverage tells you how much automated testing you have accounted for. 100% would mean that ever single line of code in your application is being covered by a unit test.

NCover is an application for .NET

Answer 4

Code coverage is a metric, showing how "well" the source code is tested. There are several types of code coverage: line coverage, function coverage, branch coverage.

In order to measure the coverage, you shall run the application either manually or by automated test.

Tools can be divided in two categories: - the ones that run the compiled code in a modified environment (like the debugger), counting the required points (functions, lines, etc.); - the ones that require special compilation - in this case the resulting binary already contains the code which actually does the counting.

There are several tools for measuring and visualizing the result, they depend from platform, from source code's language.

Please read article on Wikipedia

To provide you tools, please define for which OS and language do you use.

Answer 5

The other answers already cover what Code Coverage is. The think I'd like to stress is that you need to be careful not to treat high coverage as implicitly meaning you've tested all scenarios. It doesn't necessarily say how well you've tested the code or the quality of your tests, just that you've hit a certain percentage of code as part of the tests running.

High Code Coverage does not necessarily mean High Test Quality, but High Test Quality does mean High Code Coverage

In practice, I usually aim for 90-95% code coverage which is often achievable. The last few % are often too expensive to be worth trying to hit.

Answer 6

There are many ways to develop applications. One of those is "Extreme Programming" or "Test Driven Design (TDD)". It states that all code should be tested. Code Coverage is a means of measuring how much is tested.

I'd like to make a small remark about this: I don't think all code should be tested, nor that one should set a specific percentage of code coverage. Neither do I think that code shouldn't be tested with Unit Tests (code testing code). I do think one should decide what makes sense to test. Due to this reason I generally don't use code coverage.

One thing that some tools provide, is highlight the parts that are tested. This way you might run into some code that isn't tested but actually should be, which is the only thing I use it for.

Answer 7

Good answers.

My two cents is that there is no method of testing that catches all errors, but less testing will never catch more errors, so any testing is good. To my mind, coverage testing is not to show what code has been exercised, but to show what code has not been exercised, because that is where bugs love to lurk.

If you combine it with single-stepping, it is a very good way to review code and catch bugs. Here's an example.