Add coverage requirement for jest

[ryanhu021]

Description
As we start expanding the codebase, we want to ensure that we are creating thorough unit tests for every piece of functionality. While we don't want to enforce a strict 100% line coverage, it helps to have a minimum line requirement to ensure we aren't leaving out big chunks of code.

A good baseline to start with is 80% for all source files. This ensures the majority of our code is covered and leaves room for WIP/untestable code.

Acceptance Criteria
Jest requires a global coverage threshold of 80% for branches, functions, lines, and statements. the npm test command fails if this requirement is not met.

Steps:

• Modify the jest configuration to collect coverage from all source files in the /src folder
• Add a global coverage threshold of 80%
• Modify the npm test command in package.json to run jest --coverage instead of jest
• Ensure npm test displays the coverage report

Additional Information

• Jest configuration docs