add instructions on running individual tests (#6686)

build/run-tap

@@ -1,3 +1,8 @@
 #!/usr/bin/env bash
+if [ "$#" == 5 ]; then
+  arg="${@:0:4} ${BASH_ARGV[1]}/${BASH_ARGV[0]}"
+else
+  arg="${@}"
+fi
 
-node_modules/.bin/tap --node-arg -r --node-arg @mapbox/flow-remove-types/register --node-arg -r --node-arg @std/esm ${@}
+node_modules/.bin/tap --node-arg -r --node-arg @mapbox/flow-remove-types/register --node-arg -r --node-arg @std/esm $arg

test/README.md

@@ -10,6 +10,11 @@ There are two test suites associated with Mapbox GL JS
  - `yarn test` runs quick unit tests
  - `yarn run test-suite` runs slower integration tests
 
+ To run individual tests:
+
+ - Unit tests: `yarn test-unit path/to/file.test.js` where the path begins within the `/test/unit/` directory
+ - Render tests: `yarn test-render render-test-name`
+
 ## Writing Unit Tests
 
  - **You must not share variables between test cases.** All test fixtures must be wrapped in `create` functions. This ensures each test is run in an isolated environment.