Geoff told an anecdote which was supposed to serve as "a salutary reminder that tests need public credibility". Well, there's the first response to the question posed in the headline. National tests (in English at key stage 3, anyway) don't have any public credibility.
No one I know objects to the concept of testing. Let's hope the mooted changes introduce a more valid form of assessment.
One entirely correct point Geoff made was that "great teachers have always kept tests in perspective while continuing to enthuse and inspire their classes". As well as great, these teachers need to be brave too - it might be their head on the block come (inaccurate) results time.
The "mad tangents" to which he refers are great - but they don't look so attractive when you're being beaten over the head with a weighty and invalid league table.
Ian McNeilly, Director, National Association for the Teaching of English.