OVM Test : 

In the ovm metholdogy all tests are basically classes. And all testclasses are  extended by ovm_test class. A ovm test have following properties :

1. Unique to OVM
2. Derived from ovm_test base class
3. Tests are top level components that create the dynamic  testbench
4. They have all simulation phases
5. start_of_simulation(), run() are used to specify the run time parameters of the environment

Using OVM testcases multiple tests are compiled together and a testcase can be choosen at the run time using command line option. The constraint random testcases in the ovm are much shorter than the directed testcases. With ovm_test clss we dont need to recompile the environment again to run a new testcase which saves huge time for big verfication environements.

A testcase can be selected on the runtime by passing the addtional parameter +OVM_TESTNAME=testclass_name to the command line.

Something like this for the questa sim.

vsim -c top -do run.do +OVM_TESTNAME=mem_base_test

If +OVM_TESTNAME=test_name is specified, then an object of type ‘test_name’ is created by factory.  Here, it is presumed that the test will instantiate the test environment, or the test environment will have already been instantiated before the call to run_test().

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