lru_cache_test.py

import unittest

from lru_cache import LruCache

class LruCacheTest(unittest.TestCase):
    def test_zero_limit_is_error(self):
        self.assertRaises(ValueError, lambda: LruCache(limit=0))

    def test_set_then_get(self):
        cache = LruCache(limit=10)

        self.assertIsNone(cache.get("greeting"))
        self.assertIsNone(cache.get("parting"))

        cache.set("greeting", "hello")

        self.assertEqual(cache.get("greeting"), "hello")
        self.assertIsNone(cache.get("parting"))

    def test_limit(self):
        limit = 3
        cache = LruCache(limit=limit)

        keys = ["a", "b", "c", "d", "e"]

        for key in keys:
            cache.set(key, f"{key}-1")

        hits = 0
        for key in keys:
            if cache.get(key) is not None:
                hits += 1

        self.assertEqual(hits, limit)

    def test_eviction_order_just_inserts(self):
        cache = LruCache(limit=2)

        cache.set("a", 1)
        cache.set("b", 2)
        cache.set("c", 3)
        self.assertIsNone(cache.get("a"))

    def test_eviction_order_after_gets(self):
        cache = LruCache(limit=2)

        cache.set("a", 1)
        cache.set("b", 2)
        cache.get("a")
        cache.get("b")
        cache.get("a")
        cache.set("c", 3)
        self.assertIsNone(cache.get("b"))
        self.assertEqual(cache.get("a"), 1)
        self.assertEqual(cache.get("c"), 3)

    def test_get_refreshes_item(self):
        """Test that getting an item makes it recently used"""
        cache = LruCache(limit=2)

        cache.set("a", 1)
        cache.set("b", 2)
        
        # Access "a" to make it recently used
        cache.get("a")
        
        # Add new item - should evict "b" not "a"
        cache.set("c", 3)
        
        self.assertIsNone(cache.get("b"))  # "b" was evicted
        self.assertEqual(cache.get("a"), 1)  # "a" remains
        self.assertEqual(cache.get("c"), 3)

    def test_complex_usage_pattern(self):
        """Test LRU behavior with multiple operations"""
        cache = LruCache(limit=3)
        
        # Add initial items
        cache.set("a", 1)
        cache.set("b", 2)
        cache.set("c", 3)
        
        # Use items in various order
        cache.get("a")
        cache.get("c") 
        cache.get("b")
        cache.get("a")
        
        # Add new item - should evict least recently used ("c")
        cache.set("d", 4)
        
        self.assertIsNone(cache.get("c"))  # "c" was evicted
        self.assertEqual(cache.get("a"), 1)
        self.assertEqual(cache.get("b"), 2)
        self.assertEqual(cache.get("d"), 4)


if __name__ == "__main__":
    unittest.main()