go/src/math/rand/default_test.go

// Test that racy access to the default functions behaves reasonably.
func TestDefaultRace(t *testing.T) { … }

// doDefaultTest should be run before there have been any calls to the
// top-level math/rand functions. Make sure that we can make concurrent
// calls to top-level functions and to Seed without any duplicate values.
// This will also give the race detector a change to report any problems.
func doDefaultTest(t *testing.T, v string) { … }