5.1.2 Should wait for settings ACK

[danielkec]

5.1.2 Tests Stream concurrency limit by setting initial window size to 0.

Problem is that the test is racing against asynchronously handled flow-control on some server impls.

Test should wait for settings ACK before opening first stream.

https://github.com/summerwind/h2spec/blob/af83a65f0b6273ef38bf778d400d98892e7653d8/http2/5_1_2_stream_concurrency.go#L34-L54

[robaho]

There are more problems with this test, see https://github.com/summerwind/h2spec/issues/139