LoadingCacheTest.java

package com.zola.service.marketplace.core;

import com.github.benmanes.caffeine.cache.Caffeine;
import com.github.benmanes.caffeine.cache.LoadingCache;
import org.junit.jupiter.api.Test;

import java.util.Objects;

import static org.assertj.core.api.AssertionsForClassTypes.assertThat;

class LoadingCacheTest {

    static class KeyClass {
        private String key;

        public String getKey() {
            return key;
        }

        public void setKey(String key) {
            this.key = key;
        }

        @Override
        public int hashCode() {
            return Objects.hashCode(key);
        }

        public KeyClass(String someKey) {
            this.setKey(someKey);
        }
    }

    @Test
    void testLoadingCacheError() {
        LoadingCache<KeyClass, String> loadingCache = Caffeine.newBuilder()
                .recordStats()
                .maximumSize(2)
                .build(this::cacheLoader);

        var key1 = new KeyClass("key1");
        var key2 = new KeyClass("key2");

        assertThat(loadingCache.get(key1)).isEqualTo(key1.getKey());
        assertThat(loadingCache.get(key2)).isEqualTo(key2.getKey());

        // So far, so good. Now let's mutate the keys:
        key1.setKey("some other key1");
        key2.setKey("some other key2");
        assertThat(loadingCache.get(key1)).isEqualTo("some other key1");
        assertThat(loadingCache.get(key2)).isEqualTo("some other key2");

        // and finally, let's add a third entry to the cache, which should force eviction
        var key3 = new KeyClass("key3");
        assertThat(loadingCache.get(key3)).isEqualTo(key3.getKey());

        /*
            The test will pass, but should produce output like this:

            Apr 07, 2023 11:13:04 AM com.github.benmanes.caffeine.cache.BoundedLocalCache logIfAlive
            SEVERE: An invalid state was detected that occurs if the key's equals or hashCode was modified while it 
            resided in the cache. This violation of the Map contract can lead to non-deterministic behavior 
            (key: LoadingCacheTest$KeyClass@71d90b6e).
         */
    }

    private String cacheLoader(KeyClass keyObject) {
        return keyObject.getKey();
    }
}