An assert to affirm a method exists

gistfile1.groovy

// The signature that works out more naturally
void assertHasMethod(Object obj, String name, Class[] types) {
  def methods = obj.metaClass.respondsTo(obj, name, types)
  if(methods.isEmpty()) fail("Could not find method $name($types) on $obj")
}

// Enables [Foo,Bar,Baz] notation
void assertHasMethod(Object obj, String name, List<Class> types) {
  assertHasMethod(obj, name, types.toArray(new Class[0]))
}

This will check for both static and dynamic types. However, the dynamic types will need to be injected/configured/whatever for your test cases to detect them.