...when up to half of the output of a full-blown TDD-style project can be test code, we’re going to want to find ways to automate and streamline the effort.
We have to make a distinction about what kinds of tests we're writing and what kinds of tests we want to automate.
The TDD tests should be just enough to get to a satisfactory design. Depending on the system being constructed, you should still consider acceptance tests, including performance tests and more complete suites for functional coverage than were needed just for the design process.
We don't want to "over automate" the TDD tests since they are programmer tests, i.e. a programmer's tool for thinking.
We do want to automate the validation and verification tests because we want to eliminate boredom and error, allowing the V&V team to spend their time on activities like creative exploratory tests.