> If you have a problem with Foo If you have a problem with Foo, you instantiate a Foo inside FooTest, and then feed it problematic input. You can't instantia

> If you have a problem with Foo If you have a problem with Foo, you instantiate a Foo inside FooTest, and then feed it problematic input. You can't instantiate a Foo inside FooTest unless you can instantiate a Foo and a Bar. Foo could be a clock whose time-of-day you can't control, and Bar could be a database that you can't instantiate.