It was failing in a strange way, e.g.

panic: Buf: refcnt < 0
fatal error: panic holding locks

goroutine 19 [running]:
runtime.throw(0x5f9d65, 0x13)
        /home/kirr/src/tools/go/go/src/runtime/panic.go:605 +0x95 fp=0xc42003cc20 sp=0xc42003cc00 pc=0x452935
panic(0x5c21c0, 0x611f60)
        /home/kirr/src/tools/go/go/src/runtime/panic.go:451 +0x585 fp=0xc42003ccc8 sp=0xc42003cc20 pc=0x4524c5
lab.nexedi.com/kirr/neo/go/zodb.(*Buf).Release(0xc4200900e0)
        /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/buffer.go:112 +0x161 fp=0xc42003ccf8 sp=0xc42003ccc8 pc=0x59ebc1
lab.nexedi.com/kirr/neo/go/zodb.TestBufAllocFree(0xc4200a80f0)
        /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/buffer_test.go:111 +0x6ae fp=0xc42003cf78 sp=0xc42003ccf8 pc=0x5a137e
testing.tRunner(0xc4200a80f0, 0x600930)
        /home/kirr/src/tools/go/go/src/testing/testing.go:746 +0x16d fp=0xc42003cfd0 sp=0xc42003cf78 pc=0x51688d
runtime.goexit()
        /home/kirr/src/tools/go/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc42003cfd8 sp=0xc42003cfd0 pc=0x4835f1
created by testing.(*T).Run
        /home/kirr/src/tools/go/go/src/testing/testing.go:789 +0x569

goroutine 1 [chan receive]:
testing.(*T).Run(0xc4200a8000, 0x5f9180, 0x10, 0x600930, 0xc420051c50)
        /home/kirr/src/tools/go/go/src/testing/testing.go:790 +0x59b
testing.runTests.func1(0xc4200a8000)
        /home/kirr/src/tools/go/go/src/testing/testing.go:1004 +0xa8
testing.tRunner(0xc4200a8000, 0xc420051d90)
        /home/kirr/src/tools/go/go/src/testing/testing.go:746 +0x16d
testing.runTests(0xc420090040, 0x6ed4a0, 0x7, 0x7, 0x4159b0)
        /home/kirr/src/tools/go/go/src/testing/testing.go:1002 +0x522
testing.(*M).Run(0xc420051f20, 0x1d7ab28)
        /home/kirr/src/tools/go/go/src/testing/testing.go:921 +0x207
main.main()
        lab.nexedi.com/kirr/neo/go/zodb/_test/_testmain.go:56 +0x1d4
exit status 2
FAIL    lab.nexedi.com/kirr/neo/go/zodb 0.006s

becuase upon release object was not put back into pool, then we were
getting another object from pool, complainig but still doing
buf.Release.