Auto merge of #6888 - ehuss:debug-can_not_mix_doc_tests_and_regular_tests, r=alexcrichton
Auto merge of #6888 - ehuss:debug-can_not_mix_doc_tests_and_regular_tests, r=alexcrichton

Attempt to debug a spurious test.

See #6887.  My hope is that if it fails, the log might include a clue on what is wrong.

vojtechkral/cargo,tsurai/cargo,eminence/cargo,nipunn1313/cargo,nipunn1313/cargo,eminence/cargo,nipunn1313/cargo,tsurai/cargo,tshepang/cargo,rustyhorde/cargo,rust-lang/cargo,vojtechkral/cargo,rust-lang/cargo,tsurai/cargo,rustyhorde/cargo,vojtechkral/cargo,rust-lang/cargo,rust-lang/cargo,tshepang/cargo,tshepang/cargo,eminence/cargo,tsurai/cargo,vojtechkral/cargo,rustyhorde/cargo,rustyhorde/cargo,tshepang/cargo,tsurai/cargo,nipunn1313/cargo,eminence/cargo