TestShouldExecuteAllPendingDMLsOnClose may failed by chance

[july2993]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.
   run make test

2. What did you expect to see?
   all test pass

3. What did you see instead?

----------------------------------------------------------------------
FAIL: load_test.go:517: runSuite.TestShouldExecuteAllPendingDMLsOnClose

load_test.go:563:
    c.Assert(executed, check.HasLen, 14)
... obtained []*loader.DML = []*loader.DML{(*loader.DML)(0xc000412380), (*loader.DML)(0xc0004123c0), (*loader.DML)(0xc000412440), (*loader.DML)(0xc000412480), (*loader.DML)(0xc000412500), (*loader.DML)(0xc000412540), (*loader.DML)(0xc0004125c0), (*loader.DML)(0xc000412600)}
... n int = 14

OOPS: 51 passed, 1 FAILED
--- FAIL: Test (0.41s)
FAIL
coverage: 75.7% of statements

4. Please provide the relate downstream type and version of drainer.
   (run drainer -V in terminal to get drainer's version)
   ede19d5