test(mcp-test): deflake streamable HTTP version-negotiation integration test

- tolerate an absent MCP-Protocol-Version header in the context extractor: Map.of rejects null values while spec-correct clients legitimately omit the header on initialize requests

- await the asynchronously opened GET /mcp stream before asserting recorded calls; observed intermittently in CI as AssertionError Expected size: 3 but was: 2 (evidence: actions/run/33069467622 Jackson 2 Integration Tests)

Author: slachiewicz

mcp-test/src/test/java/io/modelcontextprotocol/common/HttpClientStreamableHttpVersionNegotiationIntegrationTests.java

@@ -4,8 +4,10 @@
 
 package io.modelcontextprotocol.common;
 
+import java.time.Duration;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.function.BiFunction;
 
 import io.modelcontextprotocol.client.McpClient;
@@ -22,6 +24,7 @@
 import org.apache.catalina.LifecycleException;
 import org.apache.catalina.LifecycleState;
 import org.apache.catalina.startup.Tomcat;
+import static org.awaitility.Awaitility.await;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 
@@ -37,8 +40,10 @@ class HttpClientStreamableHttpVersionNegotiationIntegrationTests {
 
 	private final HttpServletStreamableServerTransportProvider transport = HttpServletStreamableServerTransportProvider
 		.builder()
-		.contextExtractor(
-				req -> McpTransportContext.create(Map.of("protocol-version", req.getHeader("MCP-protocol-version"))))
+		// The MCP-Protocol-Version header may legitimately be absent on initialize
+		// requests, so a missing header must not break context extraction.
+		.contextExtractor(req -> McpTransportContext
+			.create(Map.of("protocol-version", Objects.requireNonNullElse(req.getHeader("MCP-protocol-version"), ""))))
 		.build();
 
 	private final McpSchema.Tool toolSpec = McpSchema.Tool.builder("test-tool")
@@ -72,6 +77,12 @@ void usesLatestVersion() {
 		McpSchema.CallToolResult response = client
 			.callTool(McpSchema.CallToolRequest.builder("test-tool").arguments(Map.of()).build());
 
+		// The GET /mcp stream is opened asynchronously once the initialize response
+		// creates the session, so wait for it to be recorded before asserting.
+		await().atMost(Duration.ofSeconds(5))
+			.untilAsserted(() -> assertThat(requestRecordingFilter.getCalls()).filteredOn(c -> "GET".equals(c.method()))
+				.hasSize(1));
+
 		var calls = requestRecordingFilter.getCalls();
 
 		assertThat(calls).filteredOn(c -> !c.body().contains("\"method\":\"initialize\""))