On running circle-ci for my PRs, I have observed that the TestLinkContainers test case fails sometimes for no apparent reason. On re-running the CI with cosmetic changes like whitespace/comments, the test case passes. This inconsistency seems odd for just this test case.

The failure that I see is as below:

=== RUN TestLinkContainers
time="2016-08-04T19:38:25Z" level=warning msg="Running modprobe bridge br_netfilter failed with message: , error: exec: "modprobe": executable file not found in $PATH"
--- FAIL: TestLinkContainers (0.04s)
bridge_test.go:734: Failed to create bridge: Failed to program NAT chain: Failed to inject docker in PREROUTING chain: iptables failed: iptables --wait -t nat -A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER: iptables v1.4.21: Couldn't load target `DOCKER':No such file or directory

    Try `iptables -h' or 'iptables --help' for more information.
     (exit status 2)