Cross-platform issue with npm script for running tests

[issackjohn]

When trying to run any of the npm run test:<browser> commands on a Windows machine, the following error is encountered:

'BROWSER' is not recognized as an internal or external command,
operable program or batch file.

Steps to reproduce the behavior:

1. Clone the repository on a Windows machine
2. Run npm install
3. Run npm run test:edge
4. See error

Expected behavior: The tests should run successfully.

Additional context: This issue seems to be due to the way environment variables are set in the npm script. The current script uses a syntax that works on Unix-based systems but not on Windows.