Add a ConfigBuilder for tests.
Add a ConfigBuilder for tests.

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