Test status quo for zero capacity behavior in ConcurrentLruCache

See gh-31317

spring-core/src/test/java/org/springframework/util/ConcurrentLruCacheTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,13 +21,39 @@
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
+ * Tests for {@link ConcurrentLruCache}.
+ *
  * @author Juergen Hoeller
+ * @author Sam Brannen
  */
 class ConcurrentLruCacheTests {
 
 	private final ConcurrentLruCache<String, String> cache = new ConcurrentLruCache<>(2, key -> key + "value");
 
 
+	@Test
+	void zeroCapacity() {
+		ConcurrentLruCache<String, String> cache = new ConcurrentLruCache<>(0, key -> key + "value");
+
+		assertThat(cache.sizeLimit()).isZero();
+		assertThat(cache.size()).isZero();
+
+		assertThat(cache.get("k1")).isEqualTo("k1value");
+		assertThat(cache.size()).isZero();
+		assertThat(cache.contains("k1")).isFalse();
+
+		assertThat(cache.get("k2")).isEqualTo("k2value");
+		assertThat(cache.size()).isZero();
+		assertThat(cache.contains("k1")).isFalse();
+		assertThat(cache.contains("k2")).isFalse();
+
+		assertThat(cache.get("k3")).isEqualTo("k3value");
+		assertThat(cache.size()).isZero();
+		assertThat(cache.contains("k1")).isFalse();
+		assertThat(cache.contains("k2")).isFalse();
+		assertThat(cache.contains("k3")).isFalse();
+	}
+
 	@Test
 	void getAndSize() {
 		assertThat(this.cache.sizeLimit()).isEqualTo(2);