learning-go-for-sre-interview/05-lru-cache/main_test.go

package main

import (
	"fmt"
	"sync"
	"testing"
)

func TestBasicPutGet(t *testing.T) {
	c := NewLRU(2)
	c.Put("a", 1)
	if v, ok := c.Get("a"); !ok || v.(int) != 1 {
		t.Fatalf("want (1,true), got (%v,%v)", v, ok)
	}
	if _, ok := c.Get("missing"); ok {
		t.Fatal("miss reported as hit")
	}
}

func TestEvictionOrder(t *testing.T) {
	c := NewLRU(2)
	c.Put("a", 1)
	c.Put("b", 2)
	c.Put("c", 3) // evicts a (LRU)
	if _, ok := c.Get("a"); ok {
		t.Fatal("a should have been evicted")
	}
	for _, k := range []string{"b", "c"} {
		if _, ok := c.Get(k); !ok {
			t.Fatalf("%s should still be present", k)
		}
	}
}

func TestGetRefreshesRecency(t *testing.T) {
	c := NewLRU(2)
	c.Put("a", 1)
	c.Put("b", 2)
	c.Get("a")    // a becomes MRU
	c.Put("c", 3) // must evict b, not a
	if _, ok := c.Get("a"); !ok {
		t.Fatal("a was evicted despite being MRU — Get must refresh recency")
	}
	if _, ok := c.Get("b"); ok {
		t.Fatal("b should have been evicted")
	}
}

func TestUpdateExistingKey(t *testing.T) {
	c := NewLRU(2)
	c.Put("a", 1)
	c.Put("b", 2)
	c.Put("a", 99) // update, not insert — must NOT evict
	if c.Len() != 2 {
		t.Fatalf("update inflated size: len=%d", c.Len())
	}
	if v, _ := c.Get("a"); v.(int) != 99 {
		t.Fatalf("update lost: got %v", v)
	}
	c.Put("c", 3) // evicts b (a was refreshed by the update)
	if _, ok := c.Get("b"); ok {
		t.Fatal("b should have been evicted after a's update refreshed it")
	}
}

func TestConcurrentAccess(t *testing.T) {
	c := NewLRU(64)
	var wg sync.WaitGroup
	for g := 0; g < 8; g++ {
		wg.Add(1)
		go func(g int) {
			defer wg.Done()
			for i := 0; i < 500; i++ {
				k := fmt.Sprintf("k%d", i%100)
				c.Put(k, i)
				c.Get(k)
			}
		}(g)
	}
	wg.Wait()
	if c.Len() > 64 {
		t.Fatalf("capacity exceeded under concurrency: %d", c.Len())
	}
}