Cannot instantiate Groovy class, throwing no signature of getBinding()

Question

I have a Groovy script that includes a simple class. The method in the script tries to create an instance of the class, but it's throwing:

groovy.lang.MissingMethodException: No signature of method:
TestClass.getBinding() is applicable for argument types: () values: []

The class looks like this:

class TestClass {
}

The method looks like this:

def testMethod {
    def testClass = new TestClass()
}

As soon as the code arrives at the new TestClass line, it throws the error. I've tried the class with static fields and I can read those fine, but the moment I try to instantiate it I get the error.