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Fix integration tests for roots/list #1119

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Merged
Kehrlann merged 1 commit into from
Sep 1, 2026
Merged

Fix integration tests for roots/list #1119

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Fix integration tests for roots/list 
There is a race condition where the GET /mcp SSE stream in Streamable
HTTP is established _after_ the server tries to send notifications. This
surfaces errors from the MCP client sending notifications and breaks
some integration tests.

We add a utility showing to ensure the stream is established before
sending server notifications.

Fixes #1114

Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>
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@Kehrlann
Kehrlann committed Sep 1, 2026
commit 3785d3c4d3d2162c843a2f0bb725cada175eebcf
14 changes: 11 additions & 3 deletions mcp-test/src/main/java/io/modelcontextprotocol/AbstractMcpClientServerIntegrationTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,13 @@ public abstract class AbstractMcpClientServerIntegrationTests {

abstract protected McpServer.SyncSpecification<?> prepareSyncServerBuilder();

// There is, for Streamable HTTP, a race condition between establishing the SSE stream
// and the server sending notifications. This breaks some `roots/list` tests (and
// could in theory break sampling and elicitation tests). This utility method allows
// delaying the test until the stream is opened.
protected void awaitClientStreamEstablished() {
}

@ParameterizedTest(name = "{0} : {displayName} ")
@MethodSource("clientsForTesting")
void simple(String clientType) {
Expand Down Expand Up @@ -1082,6 +1089,7 @@ void testRootsSuccess(String clientType) {

InitializeResult initResult = mcpClient.initialize();
assertThat(initResult).isNotNull();
awaitClientStreamEstablished();

assertThat(rootsRef.get()).isNull();

Expand Down Expand Up @@ -1168,7 +1176,7 @@ void testRootsNotificationWithEmptyRootsList(String clientType) {

InitializeResult initResult = mcpClient.initialize();
assertThat(initResult).isNotNull();

awaitClientStreamEstablished();
mcpClient.rootsListChangedNotification();

await().atMost(Duration.ofSeconds(5)).untilAsserted(() -> {
Expand Down Expand Up @@ -1201,7 +1209,7 @@ void testRootsWithMultipleHandlers(String clientType) {
.build()) {

assertThat(mcpClient.initialize()).isNotNull();

awaitClientStreamEstablished();
mcpClient.rootsListChangedNotification();

await().atMost(Duration.ofSeconds(5)).untilAsserted(() -> {
Expand Down Expand Up @@ -1234,7 +1242,7 @@ void testRootsServerCloseWithActiveSubscription(String clientType) {

InitializeResult initResult = mcpClient.initialize();
assertThat(initResult).isNotNull();

awaitClientStreamEstablished();
mcpClient.rootsListChangedNotification();

await().atMost(Duration.ofSeconds(5)).untilAsserted(() -> {
Expand Down
14 changes: 12 additions & 2 deletions ...t/src/test/java/io/modelcontextprotocol/server/HttpServletStreamableIntegrationTests.java
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Expand Up @@ -30,7 +30,6 @@
import org.apache.catalina.LifecycleException;
import org.apache.catalina.LifecycleState;
import org.apache.catalina.startup.Tomcat;
import org.awaitility.Awaitility;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeAll;
Expand All @@ -42,6 +41,7 @@
import reactor.test.StepVerifier;

import static org.assertj.core.api.Assertions.assertThat;
import static org.awaitility.Awaitility.await;

@Timeout(15)
class HttpServletStreamableIntegrationTests extends AbstractMcpClientServerIntegrationTests {
Expand All @@ -57,6 +57,16 @@ class HttpServletStreamableIntegrationTests extends AbstractMcpClientServerInteg

private HttpServletStreamableServerTransportProvider mcpServerTransportProvider;

@Override
protected void awaitClientStreamEstablished() {
var timeout = Duration.ofSeconds(5);
await().atMost(timeout).untilAsserted(() -> {
assertThat(MCP_SERVLET.isStreamEstablished())
.withFailMessage("[Failed to observe MCP Client connection within %s]", timeout)
.isTrue();
});
}

static Stream<Arguments> clientsForTesting() {
return Stream.of(Arguments.of("httpclient"));
}
Expand Down Expand Up @@ -151,7 +161,7 @@ void testMissingHandlerReturnsMethodNotFoundError() {
.verifyComplete();

// Wait until we've received the response
Awaitility.await().atMost(Duration.ofSeconds(1)).until(() -> response.get() != null);
await().atMost(Duration.ofSeconds(1)).until(() -> response.get() != null);

assertThat(response.get().error().code()).isEqualTo(McpSchema.ErrorCodes.METHOD_NOT_FOUND);
assertThat(response.get().error().message()).isEqualTo("Method not found: foo/bar");
Expand Down
19 changes: 18 additions & 1 deletion mcp-test/src/test/java/io/modelcontextprotocol/server/transport/TomcatTestUtil.java
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Original file line number Diff line number Diff line change
Expand Up @@ -7,14 +7,17 @@
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.util.concurrent.atomic.AtomicBoolean;

import jakarta.servlet.Filter;
import jakarta.servlet.Servlet;
import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import jakarta.servlet.http.HttpServletRequest;
import org.apache.catalina.Context;
import org.apache.catalina.Wrapper;
import org.apache.catalina.startup.Tomcat;
import org.apache.tomcat.util.descriptor.web.FilterDef;
import org.apache.tomcat.util.descriptor.web.FilterMap;
Expand All @@ -41,7 +44,7 @@ public static Tomcat createTomcatServer(String contextPath, int port, Servlet se
Context context = tomcat.addContext(contextPath, baseDir);

// Add transport servlet to Tomcat
org.apache.catalina.Wrapper wrapper = context.createWrapper();
Wrapper wrapper = context.createWrapper();
wrapper.setName("mcpServlet");
wrapper.setServlet(servlet);
wrapper.setLoadOnStartup(1);
Expand Down Expand Up @@ -78,12 +81,19 @@ public static class DelegatingServlet implements Servlet {

private volatile Servlet delegate;

// Crude way of tracking whether a GET SSE stream has been established, to ensure
// a Streamable HTTP MCP Client is connected.
// This is an approximation: it switches to "true" whenever the handler is done
// servicing a GET request - even if the request is rejected or if it's a replay.
private final AtomicBoolean sseStreamEstablished = new AtomicBoolean(false);

/**
* Sets the servlet handling subsequent requests. The delegate is not
* {@link Servlet#init(ServletConfig) initialized}, since the MCP servlet
* transports do not rely on their {@link ServletConfig}.
*/
public void setDelegate(Servlet delegate) {
this.sseStreamEstablished.set(false);
this.delegate = delegate;
}

Expand All @@ -104,6 +114,9 @@ public void service(ServletRequest request, ServletResponse response) throws Ser
throw new IllegalStateException("No delegate servlet has been set");
}
current.service(request, response);
if (request instanceof HttpServletRequest req && req.getMethod().equals("GET")) {
sseStreamEstablished.set(true);

@slachiewicz slachiewicz Aug 31, 2026 •
edited
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Might be worth one extra line in the utility's comment: the observed signal is "a GET completed through service()", which equals "listening stream registered" only because registration is synchronous inside doGet today. A replay GET (Last-Event-ID) or a rejected one (e.g. 400/404 from Accept/session checks, or protocol-version validation as proposed in #1112) would set the flag without registering a stream. Current tests hit neither, so fine as-is; just so the hook isn't over-trusted if doGet ever changes.

}
}

@Override
Expand All @@ -116,6 +129,10 @@ public void destroy() {
this.delegate = null;
}

public boolean isStreamEstablished() {
return this.sseStreamEstablished.get();
}

}

/**
Expand Down
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