Update docs.

tests/unit_tests/unit_test.md

@@ -16,10 +16,10 @@ make all
 ## Execute Tests
 For `test_common` to execute:
 ```
-./test_common
+./build/test_common
 ```
 
 For `test_common` to execute and get a `tap` conform output execute:
 ```
-./test_common --tap=test.tap
+./build/test_common --tap=test.tap
 ```