It should be understood that purpose of FitNesse is to fix the broken requirement process by enhancing collaboration and enabling deterministic executable automated tests. It can be argued that why FitNesse is needed for test driven development methodology where everything is anyway driven by tests or unit tests. Using unit testing, usually programmers make sure that their design is sound and there is no defect, but they do not necessarily give information on whether feature itself is being built according to customer expectation or not.

Advantages
There are many advantages of using FitNesse and most important of them is automated acceptance tests using FitNesse. FitNesse enables early feedback by providing mechanism to execute automated acceptance tests as often as required. Tests written in the FitNesse are deterministic, i.e they either run green or red. Most importantly, test data in FitNesse is developed either by the customers or by development or quality team with the help of customer representative. Since this data is developed from the user stories and is specified in a deterministic manner, it ensures that expectation from the system is clear to everyone.

How it is implemented??
Tables are the crux of FitNesse. Acceptance tests in FitNesse are defined in the tabular format. This deterministic tabular format is understood by the Fit library. These tests or tables are defined in terms of input and expected output data. For example, if you have to write FitNesse acceptance test case for shopping cart you might have input as some item and you can check number of items in the shopping cart is increased by one.

In order to read those table and test your application under test with the data used in these tables, you need to write Fixture Code. You can imagine that Fixture Code is a bridge between the table and application under test. It understands the language of table and use this information to exercise the functionality of application.

There are different type of table styles and corresponding fixture styles to suite your application need. These tables are created on the FitNesse test pages. If you want to execute more than one test pages, you can combine them in the test suite.

You can specify that page is a suite page by changing its page properties. You can also use setup and teardown on test pages to make sure that test environment is setup properly before starting the test suite execution and environment is cleaned after it is finished. As everything else, setup and teardown is also implemented as tables.

Tests created in FitNesse can be executed from command line as well. There are many benefits of doing that. For example, you can debug them easily, you can include these in your build script, it removes the prerequisite of starting web server to execute tests and it can generate output in HTML or XML format.

To execute FitNesse from command line, you need to use TestRunner utility. This utility can be invoked using

 java fitnesse.runner.TestRunner [options] host port page-name

[options] can be used to store results, format results, running specific tests etc.

This TestRunner offers three different formats for output. HTML, XML and a plain text format called Result format. Result format is an intermediate format used to store the data while the test is executing. These results typically goes in the temporary file and after the execution submitted to the FitNesse for formatting.                                                      More On FitNesse>>>