When the compiled version of libbson is less than the minimum version, the warning is currently masked because we raise an import error here, but then give it a different message in the except block.

This occurs when building with a version from homebrew (brew install mongo-c-driver. We should address three things:

• check the version when building using pkg-config --atleast-version=xxx libbson-1.0
• fix the handling of the version check at runtime to give the appropriate error message
• audit our docs on using the homebrew version of libbson