Include receiver type in test method names

[cweill]

If two structs implement a method with the same name, they will cause gotests to generate two tests with the same name.

Instead tests should prefix the type of the receiver to the test name.

[cweill]

On second thought, the receiver name should always be prefixed in test function names for methods. e.g.

// Method
func (f *Foo) Bar() {}
// Should output.
func TestFooBar(t *testing.T) {}