diff --git a/httpclient5-testing/src/test/java/org/apache/hc/client5/testing/async/TestAsyncConnectionTimeouts.java b/httpclient5-testing/src/test/java/org/apache/hc/client5/testing/async/TestAsyncConnectionTimeouts.java
new file mode 100644
index 0000000000..a931da7a62
--- /dev/null
+++ b/httpclient5-testing/src/test/java/org/apache/hc/client5/testing/async/TestAsyncConnectionTimeouts.java
@@ -0,0 +1,120 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+package org.apache.hc.client5.testing.async;
+
+import org.apache.hc.client5.http.ConnectTimeoutException;
+import org.apache.hc.client5.http.async.methods.SimpleHttpRequest;
+import org.apache.hc.client5.http.config.ConnectionConfig;
+import org.apache.hc.client5.http.config.RequestConfig;
+import org.apache.hc.client5.http.impl.async.CloseableHttpAsyncClient;
+import org.apache.hc.client5.http.impl.async.HttpAsyncClientBuilder;
+import org.apache.hc.client5.http.impl.nio.PoolingAsyncClientConnectionManager;
+import org.apache.hc.client5.http.impl.nio.PoolingAsyncClientConnectionManagerBuilder;
+import org.apache.hc.core5.reactor.IOReactorConfig;
+import org.junit.jupiter.api.Timeout;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.time.Duration;
+import java.time.temporal.ChronoUnit;
+import java.util.concurrent.ExecutionException;
+
+import static java.lang.String.format;
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static org.apache.hc.core5.util.TimeValue.ofMilliseconds;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class TestAsyncConnectionTimeouts {
+    private static final Duration EXPECTED_TIMEOUT = Duration.ofMillis(500);
+
+    @Timeout(5)
+    @ParameterizedTest
+    @ValueSource(strings = { "http", "https" })
+    @SuppressWarnings("deprecation")
+    void testRequestConfig(final String scheme) throws Exception {
+        try (
+            final CloseableHttpAsyncClient client = HttpAsyncClientBuilder.create()
+                .setIOReactorConfig(IOReactorConfig.custom().setSelectInterval(ofMilliseconds(50)).build())
+                .setDefaultRequestConfig(RequestConfig.custom()
+                    .setConnectTimeout(EXPECTED_TIMEOUT.toMillis(), MILLISECONDS)
+                    .build())
+                .build()
+        ) {
+            warmUpClient(client);
+            assertTimeout(getRequest(scheme), client);
+        }
+    }
+
+    @Timeout(5)
+    @ParameterizedTest
+    @ValueSource(strings = { "http", "https" })
+    void testConnectionConfig(final String scheme) throws Exception {
+        final PoolingAsyncClientConnectionManager connMgr = PoolingAsyncClientConnectionManagerBuilder.create()
+            .setDefaultConnectionConfig(
+                ConnectionConfig.custom()
+                    .setConnectTimeout(EXPECTED_TIMEOUT.toMillis(), MILLISECONDS)
+                    .build())
+            .build();
+        try (
+            final CloseableHttpAsyncClient client = HttpAsyncClientBuilder.create()
+                .setIOReactorConfig(IOReactorConfig.custom().setSelectInterval(ofMilliseconds(50)).build())
+                .setConnectionManager(connMgr)
+                .build()
+        ) {
+            warmUpClient(client);
+            assertTimeout(getRequest(scheme), client);
+        }
+    }
+
+    private static void warmUpClient(final CloseableHttpAsyncClient client) {
+        client.start();
+    }
+
+    private static SimpleHttpRequest getRequest(final String scheme) {
+        return SimpleHttpRequest.create("GET", scheme + "://198.51.100.1/ping");
+    }
+
+    private static void assertTimeout(final SimpleHttpRequest request, final CloseableHttpAsyncClient client) {
+        final long startTime = System.nanoTime();
+        final Throwable ex = assertThrows(ExecutionException.class, () -> client.execute(request, null).get())
+            .getCause();
+        final Duration actualTime = Duration.of(System.nanoTime() - startTime, ChronoUnit.NANOS);
+        assertTrue(actualTime.toMillis() > EXPECTED_TIMEOUT.toMillis() / 2,
+            format("Connection attempt timed out too soon (only %,d out of %,d ms)",
+                actualTime.toMillis(),
+                EXPECTED_TIMEOUT.toMillis()));
+        assertTrue(actualTime.toMillis() < EXPECTED_TIMEOUT.toMillis() * 2,
+            format("Connection attempt timed out too late (%,d out of %,d ms)",
+                actualTime.toMillis(),
+                EXPECTED_TIMEOUT.toMillis()));
+        assertInstanceOf(ConnectTimeoutException.class, ex);
+        assertTrue(ex.getMessage().contains(EXPECTED_TIMEOUT.toMillis() + " MILLISECONDS"), ex.getMessage());
+    }
+}
diff --git a/httpclient5-testing/src/test/java/org/apache/hc/client5/testing/sync/TestConnectionTimeouts.java b/httpclient5-testing/src/test/java/org/apache/hc/client5/testing/sync/TestConnectionTimeouts.java
new file mode 100644
index 0000000000..b327d4de17
--- /dev/null
+++ b/httpclient5-testing/src/test/java/org/apache/hc/client5/testing/sync/TestConnectionTimeouts.java
@@ -0,0 +1,107 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+package org.apache.hc.client5.testing.sync;
+
+import org.apache.hc.client5.http.ConnectTimeoutException;
+import org.apache.hc.client5.http.classic.HttpClient;
+import org.apache.hc.client5.http.classic.methods.HttpGet;
+import org.apache.hc.client5.http.classic.methods.HttpUriRequestBase;
+import org.apache.hc.client5.http.config.ConnectionConfig;
+import org.apache.hc.client5.http.config.RequestConfig;
+import org.apache.hc.client5.http.impl.classic.BasicHttpClientResponseHandler;
+import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
+import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
+import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager;
+import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
+import org.apache.hc.core5.http.ClassicHttpRequest;
+import org.junit.jupiter.api.Timeout;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.time.Duration;
+import java.time.temporal.ChronoUnit;
+
+import static java.lang.String.format;
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class TestConnectionTimeouts {
+    private static final Duration EXPECTED_TIMEOUT = Duration.ofMillis(500);
+
+    @Timeout(5)
+    @ParameterizedTest
+    @ValueSource(strings = { "http", "https" })
+    @SuppressWarnings("deprecation")
+    void testRequestConfig(final String scheme) throws Exception {
+        try (final CloseableHttpClient client = HttpClientBuilder.create()
+            .setDefaultRequestConfig(RequestConfig.custom()
+                .setConnectTimeout(EXPECTED_TIMEOUT.toMillis(), MILLISECONDS)
+                .build())
+            .build()) {
+            assertTimeout(getRequest(scheme), client);
+        }
+    }
+
+    @Timeout(5)
+    @ParameterizedTest
+    @ValueSource(strings = { "http", "https" })
+    void testConnectionConfig(final String scheme) throws Exception {
+        final PoolingHttpClientConnectionManager connMgr = PoolingHttpClientConnectionManagerBuilder.create()
+            .setDefaultConnectionConfig(
+                ConnectionConfig.custom()
+                    .setConnectTimeout(EXPECTED_TIMEOUT.toMillis(), MILLISECONDS)
+                    .build())
+            .build();
+        try (final CloseableHttpClient client = HttpClientBuilder.create().setConnectionManager(connMgr).build()) {
+            assertTimeout(getRequest(scheme), client);
+        }
+    }
+
+    private static HttpUriRequestBase getRequest(final String scheme) {
+        return new HttpGet(scheme + "://198.51.100.1/ping");
+    }
+
+    private static void assertTimeout(final ClassicHttpRequest request, final HttpClient client) {
+        final long startTime = System.nanoTime();
+        final ConnectTimeoutException ex = assertThrows(ConnectTimeoutException.class,
+            () -> client.execute(request, new BasicHttpClientResponseHandler()));
+        final Duration actualTime = Duration.of(System.nanoTime() - startTime, ChronoUnit.NANOS);
+        assertTrue(actualTime.toMillis() > EXPECTED_TIMEOUT.toMillis() / 2,
+            format("Connection attempt timed out too soon (only %,d out of %,d ms)",
+                actualTime.toMillis(),
+                EXPECTED_TIMEOUT.toMillis()));
+        assertTrue(actualTime.toMillis() < EXPECTED_TIMEOUT.toMillis() * 2,
+            format("Connection attempt timed out too late (%,d out of %,d ms)",
+                actualTime.toMillis(),
+                EXPECTED_TIMEOUT.toMillis()));
+        // Capitalization (`connect` vs `Connect`) varies by Java version
+        final String message = ex.getMessage();
+        assertTrue(message.toLowerCase().contains("connect timed out"), message);
+    }
+}