add regression tests for #377
Revert "Merge pull request #352 from gaiottino/master"

This reverts commit 553b0926ae28103475fd66e6637af855a81ddb0e, reversing
changes made to 628ab3dc6a702d87340a6fdd9715d9ef54fab786.
Merge pull request #378 from Shopify/revert_352

Revert: Add error messages for missing variables when :strict