Test Driving Interface Design
Yes, it is too much.  Testing that methods exist on a contract is both overkill and high-maintenance.  If you decide to change a method name, it breaks tests, and the test breakage doesn't tell you something useful.  Ask yourself what value you are getting out of this test.

I tend to test interfaces into existence by TDD'ing the classes that use them.  I don't think that more is useful.