Add some tests

Author: bryce-anderson

servicetalk-loadbalancer-experimental/src/test/java/io/servicetalk/loadbalancer/CorePoolConnectionPoolStrategyTest.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright © 2024 Apple Inc. and the ServiceTalk project authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.servicetalk.loadbalancer;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.function.Predicate;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.greaterThan;
+import static org.hamcrest.Matchers.hasItem;
+import static org.hamcrest.Matchers.hasSize;
+import static org.hamcrest.Matchers.not;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+class CorePoolConnectionPoolStrategyTest {
+
+    List<TestLoadBalancedConnection> makeConnections(int size) {
+        List<TestLoadBalancedConnection> result = new ArrayList<>(size);
+        for (int i = 0; i < size; i++) {
+            result.add(TestLoadBalancedConnection.mockConnection("address-" + i));
+        }
+        return result;
+    }
+
+    @Test
+    void selectsHosts() {
+        List<TestLoadBalancedConnection> connections = makeConnections(1);
+        ConnectionPoolStrategy<TestLoadBalancedConnection> strategy =
+                new CorePoolConnectionPoolStrategy<>(1, false);
+        assertNotNull(strategy.select(connections, c -> true, null));
+    }
+
+    @Test
+    void prefersCorePool() {
+        List<TestLoadBalancedConnection> connections = makeConnections(10);
+        ConnectionPoolStrategy<TestLoadBalancedConnection> strategy =
+                new CorePoolConnectionPoolStrategy<>(5, false);
+        Set<TestLoadBalancedConnection> selected = new HashSet<>();
+        for (int i = 0; i < 100; i++) {
+            selected.add(strategy.select(connections, c -> true, null));
+        }
+        // Commonly we should have more than one element in strategy, although we can expect it to contain a single
+        // element with a probability of 0.2^99 or ~6e-70.
+        assertThat(selected, hasSize(greaterThan(1)));
+
+        // We should not have selected any of the non-core pool connections.
+        for (int i = 5; i < 10; i++) {
+            assertThat(selected, not(hasItem(connections.get(i))));
+        }
+    }
+
+    @Test
+    void spillsIntoOverflow() {
+        List<TestLoadBalancedConnection> connections = makeConnections(6);
+        ConnectionPoolStrategy<TestLoadBalancedConnection> strategy =
+                new CorePoolConnectionPoolStrategy<>(5, false);
+        Set<TestLoadBalancedConnection> corePoolCxns = new HashSet<>();
+        for (int i = 0; i < 5; i++) {
+            corePoolCxns.add(connections.get(i));
+        }
+        Predicate<TestLoadBalancedConnection> selector = (TestLoadBalancedConnection c) -> !corePoolCxns.contains(c);
+        assertEquals(connections.get(5), strategy.select(connections, selector, null));
+    }
+}