Fixed deprecated is_true in tests

[KentonWhite]

Types of change

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Other (documentation etc)

Pull request checklist

• [ ] Add functionality
• [x] Add tests
• [ ] Update documentation in man
• [ ] Update website documentation

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Proposed changes

is_true is deprecated and throwing warnings. Refactored tests so that no warnings are generated from is_true