Honest question. What's the value of a test like this?

    class MyObjectBuilder
      def create(object)
        if validator.valid?(object)
          factory.save(object)
        else
          raise "invalid"
        end
      end
     end

     def object_builder_test_success
       object_builder.mock(validator, mock_validator)
       object_builder.mock(factory, mock_factory)
 
       expect_method_call(validator.validate).return(true)
       expect_method_call(factory.save).return(true)

       object_builder.create(object)
    end

    def object_builder_test_failure
       object_builder.mock(validator, mock_validator)
       object_builder.mock(factory, mock_factory)
 
       expect_method_call(validator.validate).return(false)

       assert_raise(object_builder.create(object))
    end

This test is both extremely typical for strong advocates of TDD and "testable" designs, and also almost completely useless in my mind. The test is literally a more pained version of the implementation of the method (not to mention that there's typically a lot more ceremony around setting up mocks than my pseudocode indicates)

It adds value in the sense that if someone randomly types garbage into that file it will break, but it acts as a barrier to refactoring or business requirements change, as pretty much nothing but the exact implementation of the method will satisfy the test, and offers no documentation benefit over the code itself.

Lol I was on a Ruby project like this, I said these tests are tautologies since we're verbosely rewriting the implementation as a test. My yearly review from that project? "Bill does not understand unit testing"

Nobody gets fired for writing too many tests.

There is no value in a test like this. This is basically a test of a precondition (object must be valid). In fact there is not much value in the entire if statement since it is also testing a precondition. That leaves:

    def create(object)
      factory.save(object)
    end

which is just simple delegation. Perhaps just inline the call to create and get rid of the entire class, method, and tests.

It is a waste of time testing for a pre-condition. Ensuring a pre-condition is the responsibility of the caller and tests in that part of the code, or integration tests, should be responsible for identifying problems in that regard.

And now the burden of changing tests prevents any meaningful refactoring.