The suite that got slower because of one fixture

A test suite that went from four minutes to eleven over six weeks, with no test added that was individually slow.

$ ./bin/slowest junit.xml | head -3
  0.412s  OrderFlowTest::testCheckout
  0.408s  OrderFlowTest::testRefund
  0.401s  InvoiceTest::testTotals

# nothing stands out. but:
$ grep -c 'seedRealisticDistribution' tests/
188

# a seeder added in July, creating 5 customers with
# 900 orders each, called from a base class that 188
# tests inherit.

A fixture that is individually reasonable and inherited by half the suite is invisible in a slowest-tests report, because it makes everything slightly slower rather than anything much slower. The measurement that finds it is total time divided by test count over the weeks — the per-test mean went from 0.17s to 0.47s, and that number is the one worth graphing.