Comparison
Blocking data testvsData expectation
Blocking data test
the failed check stops the pipeline so the bad numbers never reach the dashboard, and someone gets paged instead.
A data test whose failure halts publication rather than merely recording a warning. Choosing which tests block is the whole design: block on everything and the pipeline stops nightly, block on nothing and the tests are decoration. The useful rule is that a test blocks when serving wrong data is worse than serving stale data, which is a question for the consumer.
Full entry →Data expectation
you write down that this column should be between zero and one hundred and that ninety-nine percent of rows should have an email, and it is checked automatically.
A declarative statement of what data should look like, expressed as a rule and evaluated against a dataset. Writing expectations is where most of the value is, because the act of stating them surfaces assumptions nobody had said out loud. The recurring practical problem is thresholds: an expectation with no tolerance fails on the first legitimate outlier and is then disabled forever.
Full entry →