“V” Model

Each phase has corresponding test or validation counterpart

 ----------------                -------------
|Requirements    |              |  Acceptance |
|     Analysis   |<------------>|Test         |
 ----------------                -------------
          \                              /
           \                            /
        -----------            -------------
       | System    |<-------->|  Integration| 
       |   Design  |          |Test         |
        -----------            -------------
              \                     /
               \                   /
            ---------         -------
           |Program  |<----->|  Unit |
           |  Design |       |Test   |
            ---------         -------
                  \            /
                   \          / 
                  --------------
                 |Implementation|
                  --------------

Reference : http://en.wikipedia.org