What is the most effective way to measure test-driven development?

The most effective way to measure Test-Driven Development (TDD) is by assessing the test coverage and the reliability of the tests. Track the percentage of code covered by tests and the ability of tests to catch defects. Additionally, monitor the frequency and success of test executions. A high test coverage and successful test runs indicate effective TDD practices, contributing to a robust and reliable codebase.

Test coverage as a metric has very little to do with TDD. Making test coverage into a goal will result in engineers gaming the metric, resulting in bad tests and lots of wasted effort. As others have said, the primary metric to optimise for in TDD is feedback cycle time. The tests of the app should run fast - ideally within 5 seconds. Any app that has a feedback cycle of more than 10 minutes will be very painful to do TDD on. Code coverage is also misleading because there are many different kinds of code coverage - function, statement, edge and condition coverage. Often the coverage used is statement coverage which doesn't properly cover every edge case.

Forget about coverage, it is the wrong metric to be optimising. The key is rapid feedback cycles: - commits should be small in behavior - commits should have tests covering that behavior - ensure the tests do not prevent refactoring

Quality is a needlessly loaded word in this context. Let's say quality is you being able to deliver value faster. Interchangeably for newly written or modified parts of your codebase. The bottom line measure for holistic DevOps agility is having tests in the language of the public API (or user) and having them run fast and on every touch-point for every developer (line written, pre commit, post commit, at merge and pre deploy).

Failing tests are bug that made it past your business requirements and design phase. Each failing test tells you something useful about your system (including the tests). Never trust a test that you did not see fail. Ensure your test assertion messages give meaningful insights into how to fix a problem. Any test that takes a long time to run should be removed and replaced.

Instead of being obsessed with metrics and the rates listed above, treat tests as a black box and assume the engineer coming to them knows nothing about the system. Feedback of course is important. Tests should make it obvious what failed and why. This can be verified by making sure the failure message makes sense to a human at the first step of TDD - the failure.

Tests don't by themselves deliver value to the stakeholders *directly*. In order to build a product you need to build a pipeline. In order to operate that pipeline you need tests. The tests provide value to the team: - knowing your code is mergeable is valuable - knowing your code has no regressions is valuable - knowing your code is documented by tests is valuable - knowing the tests retain refactoring ability is valuable - knowing the developer's test-covered some crucial corner cases is valuable The stakeholder ROI comes figuring out what you built was unnecessary and being able to safely remove it without making a mess. Code is a liability, make it easy to remove.

TDD is not an aspect of culture. That's like saying a socket wrench is part of the culture of a plumbing company. It makes no sense. TDD is a tool to give useful feedback to engineers and, indirectly, to stakeholders, on what the system is designed to do and whether changes have damaged the system. Being obsessed with metrics around TDD as this article implies will lead to undesirable unintended consequences. The whole premise of this article is flawed.

TDD in itself is not a crucial aspect of your team's culture at all stages. There will be times when a larger constraint will present itself and the needs of your team members instill a need to change your processes, perhaps even drop TDD (though that is rarely objectively necessary). Respect your team members. Respect your users. Respect yourself. You don't need to respect TDD.