Create tests for Toast component

[lindapaiste]

Should be reviewed/merged after #2329

Changes:

• Create unit tests for the end-to-end behavior of the Toast (check that it can be opened and closed).
• Add an ARIA role to the Toast. I used status rather than alert because the lower priority seemed like it made more sense.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[raclim]

Thanks for working on this!