Finally found the source of the problem. I ended up attaching some metadata to the grpc call to DropAll to identify where each call was coming from. I then used tcpdump to capture the network packets from and to the dgraph alpha server and inspected them in wireshark. I was seeing integration tests from different suites running at the same time.
It turns out that even if we don’t use t.Parallel() in our tests, tests from different packages will execute in parallel according to the GOMAXPROCS environment variable.
The solution is to use go test -p 1 ./.... The -p 1 flag disables all parallelism.