Create a directory called ArduinoUnit under <arduino installation directory>\libraries.

Copy everything from the src directory to this new directory.

Open a sketch in arduino and click Sketch | Import Library | ArduinoUnit to start unit testing.

For example, try this simple unit testing sketch:

    #include <ArduinoUnit.h>

    // Create test suite
    TestSuite suite;

    void setup() {
    }

    // Create a test called 'addition' in the test suite
    test(addition) {
        assertEquals(3, 1 + 2);
    }

    void loop() {
        // Run test suite, printing results to the serial port
        suite.run();
    }

Upload this sketch to the Arduino (using the 'Upload' button, 
  File | Upload to I/O Board or Ctrl+U).

Turn on the Serial Monitor (using the 'Serial Monitor' button, Tools | Serial Monitor or 
  Ctrl+Shift+M) and expect to see the following:

    Running test suite...
    Tests run: 1 Successful: 1 Failed: 0

FAQ
---

1. Q. I'm getting an error message like:
          1: error: pasting "test_" and ""something"" does not give a valid preprocessing token
        when I 'Verify' or 'Upload to I/O Board' my sketch. How can I fix this?

   A. You have declared a test like this with the name in quotes:

          test("something") {
              // ...
          }

      The name of the test must not be quoted. i.e. it should look like this:

          test(something) {
              // ...
          }

2. Q. I'm getting an error message like:
          error: redefinition of 'SuiteAppender test_a_appender' In function 'void test_a(Test&)':
        when I 'Verify' or 'Upload to I/O Board' my sketch. How can I fix this?

   A. You have two or more tests declared with the same name. For example:

          test(a) {
              // ...
          }
          
          test(a) {
              // ...
          }

      The names of all tests in the same sketch must be unique. This is true even if they are in 
         different test suites.

3. Q. I'm trying to write a custom assertion function but I keep getting an error message like:
          error: '__test__' was not declared in this scope
        when I 'Verify' or 'Upload to I/O Board' my sketch. How can I fix this?

   A. You have probably defined a custom assertion function such as the following:

          void assertStringsEqual(const char* expected, const char* actual) {
              assertEquals(strlen(expected), strlen(actual));
              for (int i = 0; i < strlen(expected); i++) {
                  assertEquals(expected[i], actual[i]);
              }
          }
          
      and are trying to use it like this from within a test function:
       
          assertStringsEqual("expected string", actualString);
          
      To fix this you need to add a 'Test& __test__' parameter to the signature of the custom 
      assertion function, for example:
      
          void assertStringsEqual(Test& __test__, const char* expected, const char* actual) {
              assertEquals(strlen(expected), strlen(actual));
              for (int i = 0; i < strlen(expected); i++) {
                  assertEquals(expected[i], actual[i]);
              }
          }

      and add '__test__' as the relevant argument when you call it, for example:
      
          assertStringsEqual(__test__, "expected string", actualString);

4. Q. I'm trying to use a custom assertion function but I keep getting an error message like:
          error: '<custom_assertion_function>' was not declared in this scope
        when I 'Verify' or 'Upload to I/O Board' my sketch. How can I fix this?

   A. You need to define the custom assertion function above where it is being used or 
        forward-declare it, for example:
        
          // Forward declare custom assertion
          void assertStringsEqual(Test& __test__, const char* expected, const char* actual);

          // ...
          
          test(something) {
              // Use custom assertion
              assertStringsEqual(__test__, "expected string", actualString);
          }
          
          // ...

          // Define custom assertion
          void assertStringsEqual(Test& __test__, const char* expected, const char* actual) {
              assertEquals(strlen(expected), strlen(actual));
              for (int i = 0; i < strlen(expected); i++) {
                  assertEquals(expected[i], actual[i]);
              }
          }

Version History
---------------
Version 1.4.2 (2 October 2011)
    Features added:
        Support for Arduino 1.0 environment (check for arduino version to include correct header)

Version 1.4.1 (13 June 2011)
    Bugs fixed:
	    Issue 2 - Compilation error on Arduino 0022
        Issue 3 - Incomplete MIT license terms

Version 1.4 (28 June 2009)
    Features added:
        Checks and reporting on heap allocation failures.

        Example of using ArduinoUnit to check the correct functioning of digital I/O pins 2-13.

    Bugs fixed:
        Each failed assertion counts as a single test function failure. Two failed assertions
        in the same test function double-count the failure. Since the usual case is that 
        failing assertions short-cut a test function execution by returning this is only
        noticeable where a test function calls other functions which perform the assertions.

        Stack/heap collisions are not reported and cause incorrect behaviour, reporting (for 
        example):
            Equality assertion failed in 'nameReported' on line 310: expected 
              '9599460892�leFailingAssertion' but was '0'

Version 1.3 (01 June 2009)
    Features added:
        Allowed the use of variables named 'test' in test functions. The name __test__ is now a 
          reserved word and if used as a variable name within a test function (e.g. like this:
            test(name) {
                int __test__ = 0;
            }    
          ) verifying or uploading the sketch will cause the following compilation error:
            error: declaration of 'int __test__' shadows a parameter
            
        Added keyword highlighting for 'TestSuite', 'run', 'test', 'assertTrue', 'assertEquals' 
          and '__test__'.

    Bugs fixed:
        Line numbers of failing boolean assertions (assertTrue()) are 3 greater than the real
        line numbers (line numbers reported for failing equality assertions are correct)

Version 1.2 (29 May 2009)
    Features added:
        Reduced the compiled size of sketches using ArduinoUnit:
            Usage                      From (bytes)    To (bytes)    Reduction (bytes)
            -----------------------    ------------    ----------    -----------------
            Including ArduinoUnit.h    2014            1906          108
            Creating a test suite       766             774           -8
            Running a test suite        132             120           12
            -----------------------    ------------    ----------    -----------------
            Total                      2912            2800          112

    Bugs fixed:
        Using Sketch | Import Library | ArduinoUnit #includes all the header files in the 
          ArduinoUnit directory rather than just ArduinoUnit.h

Version 1.1 (27 May 2009)
    Bugs fixed:
        When using multiple test suites in a sketch all assertions are reported in against the last 
          defined suite.

Version 1.0 (25 May 2009)
    Features added:
        Simple test definition and execution
        Boolean assertions
        Integer equality assertions
        Default reporting of results to the serial port
        Ability to customize result reporting (e.g. where serial port is being used by the code under test)
        Support for multiple (optionally named) test suites