triangle: add test template #1998

Task

Create a test template file for triangle

Details

1. If this is your first time contributing to this repository, welcome!
   • Contributing to a repository on GitHub requires a fork
2. Create a branch on your local repository called triangle-add-test-template
   • Run: git checkout -b triangle-add-test-template
3. Clone problem-specifications repository; this is used to populate the template
   • Run: git clone https://github.com/exercism/problem-specifications ../problem-specifications
4. Create exercises/triangle/.meta/template.j2
   • See Generator Documentation for more information
5. Generate test file from new template
   • Run: bin/generate_tests.py triangle

At this point, if the generator fails, or you are otherwise stuck,
please feel free to reach out! It is perfectly acceptable to submit
an incomplete PR in order to get feedback or assistance.

Resources

• Contributing Guide
• Generator Documentation
• Closing issues using keywords