Attempt to fix flaky Zipkin test

Update `ZipkinHttpClientSenderTests` to use one mock server per test
rather than a shared static. For some reason the mock server sometimes
seems to get itself in a deadlock state which causes the client to
fail with a `HttpTimeoutException`.

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/zipkin/ZipkinHttpClientSenderTests.java

@@ -28,10 +28,7 @@ import java.util.function.Consumer;
 
 import okhttp3.mockwebserver.MockResponse;
 import okhttp3.mockwebserver.MockWebServer;
-import okhttp3.mockwebserver.QueueDispatcher;
 import okhttp3.mockwebserver.RecordedRequest;
-import org.junit.jupiter.api.AfterAll;
-import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import zipkin2.reporter.BytesMessageSender;
@@ -52,32 +49,23 @@ import static org.assertj.core.api.Assertions.assertThatIOException;
  */
 class ZipkinHttpClientSenderTests extends ZipkinHttpSenderTests {
 
-	private static ClearableDispatcher dispatcher;
+	private MockWebServer mockBackEnd;
 
-	private static MockWebServer mockBackEnd;
-
-	static String zipkinUrl;
-
-	@BeforeAll
-	static void beforeAll() throws IOException {
-		dispatcher = new ClearableDispatcher();
-		mockBackEnd = new MockWebServer();
-		mockBackEnd.setDispatcher(dispatcher);
-		mockBackEnd.start();
-		zipkinUrl = mockBackEnd.url("/api/v2/spans").toString();
-	}
-
-	@AfterAll
-	static void afterAll() throws IOException {
-		mockBackEnd.shutdown();
-	}
+	private String zipkinUrl;
 
 	@Override
 	@BeforeEach
 	void beforeEach() throws Exception {
+		this.mockBackEnd = new MockWebServer();
+		this.mockBackEnd.start();
+		this.zipkinUrl = this.mockBackEnd.url("/api/v2/spans").toString();
 		super.beforeEach();
-		clearResponses();
-		clearRequests();
+	}
+
+	@Override
+	void afterEach() throws IOException {
+		super.afterEach();
+		this.mockBackEnd.shutdown();
 	}
 
 	@Override
@@ -92,12 +80,12 @@ class ZipkinHttpClientSenderTests extends ZipkinHttpSenderTests {
 	ZipkinHttpClientSender createSender(HttpEndpointSupplier.Factory endpointSupplierFactory, Encoding encoding,
 			Duration timeout) {
 		HttpClient httpClient = HttpClient.newBuilder().connectTimeout(timeout).build();
-		return new ZipkinHttpClientSender(encoding, endpointSupplierFactory, zipkinUrl, httpClient, timeout);
+		return new ZipkinHttpClientSender(encoding, endpointSupplierFactory, this.zipkinUrl, httpClient, timeout);
 	}
 
 	@Test
 	void sendShouldSendSpansToZipkin() throws IOException, InterruptedException {
-		mockBackEnd.enqueue(new MockResponse());
+		this.mockBackEnd.enqueue(new MockResponse());
 		List<byte[]> encodedSpans = List.of(toByteArray("span1"), toByteArray("span2"));
 		this.sender.send(encodedSpans);
 		requestAssertions((request) -> {
@@ -109,7 +97,7 @@ class ZipkinHttpClientSenderTests extends ZipkinHttpSenderTests {
 
 	@Test
 	void sendShouldSendSpansToZipkinInProto3() throws IOException, InterruptedException {
-		mockBackEnd.enqueue(new MockResponse());
+		this.mockBackEnd.enqueue(new MockResponse());
 		List<byte[]> encodedSpans = List.of(toByteArray("span1"), toByteArray("span2"));
 		try (BytesMessageSender sender = createSender(Encoding.PROTO3, Duration.ofSeconds(10))) {
 			sender.send(encodedSpans);
@@ -127,22 +115,22 @@ class ZipkinHttpClientSenderTests extends ZipkinHttpSenderTests {
 	 */
 	@Test
 	void sendUsesDynamicEndpoint() throws Exception {
-		mockBackEnd.enqueue(new MockResponse());
-		mockBackEnd.enqueue(new MockResponse());
-		try (TestHttpEndpointSupplier httpEndpointSupplier = new TestHttpEndpointSupplier(zipkinUrl)) {
+		this.mockBackEnd.enqueue(new MockResponse());
+		this.mockBackEnd.enqueue(new MockResponse());
+		try (TestHttpEndpointSupplier httpEndpointSupplier = new TestHttpEndpointSupplier(this.zipkinUrl)) {
 			try (BytesMessageSender sender = createSender((endpoint) -> httpEndpointSupplier, Encoding.JSON,
 					Duration.ofSeconds(10))) {
 				sender.send(Collections.emptyList());
 				sender.send(Collections.emptyList());
 			}
-			assertThat(mockBackEnd.takeRequest().getPath()).endsWith("/1");
-			assertThat(mockBackEnd.takeRequest().getPath()).endsWith("/2");
+			assertThat(this.mockBackEnd.takeRequest().getPath()).endsWith("/1");
+			assertThat(this.mockBackEnd.takeRequest().getPath()).endsWith("/2");
 		}
 	}
 
 	@Test
 	void sendShouldHandleHttpFailures() throws InterruptedException {
-		mockBackEnd.enqueue(new MockResponse().setResponseCode(500));
+		this.mockBackEnd.enqueue(new MockResponse().setResponseCode(500));
 		assertThatException().isThrownBy(() -> this.sender.send(Collections.emptyList()))
 			.withMessageContaining("Expected HTTP status 2xx, got 500");
 		requestAssertions((request) -> assertThat(request.getMethod()).isEqualTo("POST"));
@@ -154,7 +142,7 @@ class ZipkinHttpClientSenderTests extends ZipkinHttpSenderTests {
 		// This is gzip compressed 10000 times 'a'
 		byte[] compressed = Base64.getDecoder()
 			.decode("H4sIAAAAAAAA/+3BMQ0AAAwDIKFLj/k3UR8NcA8AAAAAAAAAAAADUsAZfeASJwAA");
-		mockBackEnd.enqueue(new MockResponse());
+		this.mockBackEnd.enqueue(new MockResponse());
 		this.sender.send(List.of(toByteArray(uncompressed)));
 		requestAssertions((request) -> {
 			assertThat(request.getMethod()).isEqualTo("POST");
@@ -168,35 +156,15 @@ class ZipkinHttpClientSenderTests extends ZipkinHttpSenderTests {
 	void shouldTimeout() throws IOException {
 		try (BytesMessageSender sender = createSender(Encoding.JSON, Duration.ofMillis(1))) {
 			MockResponse response = new MockResponse().setResponseCode(200).setHeadersDelay(100, TimeUnit.MILLISECONDS);
-			mockBackEnd.enqueue(response);
+			this.mockBackEnd.enqueue(response);
 			assertThatIOException().isThrownBy(() -> sender.send(Collections.emptyList()))
 				.withMessageContaining("timed out");
 		}
 	}
 
 	private void requestAssertions(Consumer<RecordedRequest> assertions) throws InterruptedException {
-		RecordedRequest request = mockBackEnd.takeRequest();
+		RecordedRequest request = this.mockBackEnd.takeRequest();
 		assertThat(request).satisfies(assertions);
 	}
 
-	private static void clearRequests() throws InterruptedException {
-		RecordedRequest request;
-		do {
-			request = mockBackEnd.takeRequest(0, TimeUnit.SECONDS);
-		}
-		while (request != null);
-	}
-
-	private static void clearResponses() {
-		dispatcher.clear();
-	}
-
-	private static final class ClearableDispatcher extends QueueDispatcher {
-
-		void clear() {
-			getResponseQueue().clear();
-		}
-
-	}
-
 }