add dummy test coverage.

_tool/test-coverage.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+# WARNING:
+# This is way too slow. Probably because of cryptography with coverage colleciton.
+# https://github.com/dart-lang/coverage/issues/261
+
+set -xeu
+
+cd "${0%/*}"/..
+
+
+pub get
+pub global activate test_coverage
+
+fail=false
+pub global run test_coverage || fail=true
+echo "fail=$fail"
+bash <(curl -s https://codecov.io/bash) -f coverage/lcov.info
+
+test "$fail" == "true" && exit 1
+
+echo "Success 🎉️"
+
+exit 0