learning-go-for-sre-interview/99-experiments/global-ratelimit/limiter/limiter_test.go

package limiter

import (
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

func TestBurstThenDeny(t *testing.T) {
	s := NewStore(Limit{Rate: 1, Burst: 3}, nil)
	for i := 0; i < 3; i++ {
		if !s.Allow("k", 1).Allowed {
			t.Fatalf("request %d within burst should be allowed", i)
		}
	}
	d := s.Allow("k", 1)
	if d.Allowed {
		t.Fatal("4th immediate request should be denied")
	}
	if d.RetryAfter <= 0 || d.RetryAfter > time.Second {
		t.Fatalf("retry-after should be ~1s at rate 1, got %v", d.RetryAfter)
	}
}

func TestRefill(t *testing.T) {
	s := NewStore(Limit{Rate: 20, Burst: 1}, nil)
	if !s.Allow("k", 1).Allowed {
		t.Fatal("initial token missing")
	}
	if s.Allow("k", 1).Allowed {
		t.Fatal("should be empty immediately after")
	}
	time.Sleep(120 * time.Millisecond)
	if !s.Allow("k", 1).Allowed {
		t.Fatal("should have refilled")
	}
}

func TestBurstIsCapped(t *testing.T) {
	s := NewStore(Limit{Rate: 1000, Burst: 2}, nil)
	time.Sleep(50 * time.Millisecond)
	allowed := 0
	for i := 0; i < 10; i++ {
		if s.Allow("k", 1).Allowed {
			allowed++
		}
	}
	if allowed > 2 {
		t.Fatalf("idle time built credit beyond burst: %d", allowed)
	}
}

func TestKeysAreIsolatedAndOverridden(t *testing.T) {
	s := NewStore(Limit{Rate: 0.0001, Burst: 1}, map[string]Limit{"vip": {Rate: 0.0001, Burst: 5}})
	if !s.Allow("a", 1).Allowed || s.Allow("a", 1).Allowed {
		t.Fatal("key a should allow exactly one")
	}
	if !s.Allow("b", 1).Allowed {
		t.Fatal("key b must have its own bucket")
	}
	for i := 0; i < 5; i++ {
		if !s.Allow("vip", 1).Allowed {
			t.Fatalf("vip request %d should be allowed (burst 5)", i)
		}
	}
	if s.Allow("vip", 1).Allowed {
		t.Fatal("vip 6th should be denied")
	}
	if got := s.Stats().Keys; got != 3 {
		t.Fatalf("expected 3 keys, got %d", got)
	}
}

func TestAllowN(t *testing.T) {
	s := NewStore(Limit{Rate: 0.0001, Burst: 10}, nil)
	if !s.Allow("k", 7).Allowed {
		t.Fatal("7 of 10 should be allowed")
	}
	if s.Allow("k", 4).Allowed {
		t.Fatal("4 more (3 left) should be denied")
	}
	if !s.Allow("k", 3).Allowed {
		t.Fatal("exactly 3 left should be allowed")
	}
}

func TestConcurrentNoOverAdmission(t *testing.T) {
	s := NewStore(Limit{Rate: 0.0001, Burst: 100}, nil)
	var allowed atomic.Int64
	var wg sync.WaitGroup
	for i := 0; i < 50; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for j := 0; j < 10; j++ {
				if s.Allow("shared", 1).Allowed {
					allowed.Add(1)
				}
			}
		}()
	}
	wg.Wait()
	if got := allowed.Load(); got != 100 {
		t.Fatalf("expected exactly 100 admissions, got %d", got)
	}
	st := s.Stats()
	if st.Allowed != 100 || st.Denied != 400 {
		t.Fatalf("stats mismatch: %+v", st)
	}
}

func TestSweepEvictsIdleOnly(t *testing.T) {
	s := NewStore(Limit{Rate: 1000, Burst: 1}, nil)
	s.Allow("old", 1)
	time.Sleep(30 * time.Millisecond)
	s.Allow("fresh", 1)
	if n := s.Sweep(20 * time.Millisecond); n != 1 {
		t.Fatalf("expected 1 evicted, got %d", n)
	}
	if got := s.Stats().Keys; got != 1 {
		t.Fatalf("expected 1 key left, got %d", got)
	}
	// evicted key comes back full, which is what an idle bucket would be anyway
	if !s.Allow("old", 1).Allowed {
		t.Fatal("recreated bucket should start full")
	}
}