You can run Golang tests in parallel by calling t.Parallel() in the very beginning of a test function. For example:

func TestRunThisInParallel(t *testing.T) {
  t.Parallel()
  // the actual test
}

Tests for a specific package by default are executed sequentially, but then using t.Parallel() a test is marked as safe for parallel execution within the test package.
Only those tests marked as parallel will be executed in parallel so ideally you should mark more than one.

You can use the -parallel flag when running go test if you need more fine-grained control over the number of tests to run in parallel. It defaults to GOMAXPROCS.