test(otel): Add a smoke test that runs an app with the built agent (#6269)

The agent had no tests; only the sample system tests exercised it. The
test launches a JDK-only app in a child JVM with the agent attached and
asserts that an incoming request reaches MockSentryServer as an
http.server transaction from the agent SDK.

The app runs in a child JVM so the test's own JVM stays uninstrumented.
Otherwise the agent would turn the test's HTTP calls and the mock server
into spans. The agent jar is wired as a test input, so the test reruns
whenever the jar changes.

Adding Kotlin for the test enrolls the module in API validation, hence
the new API dump.

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: runningcode

sentry-opentelemetry/sentry-opentelemetry-agent/api/sentry-opentelemetry-agent.api

@@ -0,0 +1,4 @@
+public final class io/sentry/opentelemetry/agent/AgentMarker {
+	public fun <init> ()V
+}
+

sentry-opentelemetry/sentry-opentelemetry-agent/build.gradle.kts

@@ -1,12 +1,18 @@
 import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 plugins {
   `java-library`
   id("io.sentry.animalsniffer")
   id("io.sentry.javadoc")
+  alias(libs.plugins.kotlin.jvm)
   alias(libs.plugins.shadow)
 }
 
+tasks.named<KotlinCompile>("compileKotlin") {
+  compilerOptions.jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_1_8
+}
+
 fun relocatePackages(shadowJar: ShadowJar) {
   // rewrite dependencies calling Logger.getLogger
   shadowJar.relocate("java.util.logging.Logger", "io.opentelemetry.javaagent.bootstrap.PatchLogger")
@@ -76,6 +82,11 @@ dependencies {
   bootstrapLibs(projects.sentryOpentelemetry.sentryOpentelemetryBootstrap)
   javaagentLibs(projects.sentryOpentelemetry.sentryOpentelemetryAgentcustomization)
   upstreamAgent(libs.otel.javaagent)
+
+  testImplementation(projects.sentryTestSupport)
+  testImplementation(kotlin(Config.kotlinStdLib))
+  testImplementation(libs.kotlin.test.junit)
+  testImplementation(libs.google.truth)
 }
 
 fun isolateClasses(jars: Iterable<File>): CopySpec = copySpec {
@@ -197,6 +208,22 @@ tasks {
   }
 
   assemble { dependsOn(shadowJar) }
+
+  test {
+    jvmArgumentProviders.add(
+      objects.newInstance<AgentJarArgument>().apply {
+        agentJar.set(shadowJar.flatMap { it.archiveFile })
+      }
+    )
+  }
+}
+
+// Tests launch apps with the built agent attached, so the agent jar is a test input.
+abstract class AgentJarArgument : CommandLineArgumentProvider {
+  @get:InputFile @get:PathSensitive(PathSensitivity.NONE) abstract val agentJar: RegularFileProperty
+
+  override fun asArguments() =
+    listOf("-Dsentry.test.agentJar=${agentJar.get().asFile.absolutePath}")
 }
 
 tasks.named("distZip").configure { this.dependsOn("jar") }

sentry-opentelemetry/sentry-opentelemetry-agent/src/test/java/io/sentry/opentelemetry/agent/fixture/HelloServer.java

@@ -0,0 +1,34 @@
+package io.sentry.opentelemetry.agent.fixture;
+
+import com.sun.net.httpserver.HttpServer;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+
+/**
+ * An app for the agent to instrument. It only uses the JDK, so a test can run it with nothing but
+ * this class on the classpath, and it writes its port to the file named by the first argument.
+ */
+public final class HelloServer {
+  public static void main(final String[] args) throws IOException {
+    final HttpServer server =
+        HttpServer.create(new InetSocketAddress(InetAddress.getByName("127.0.0.1"), 0), 0);
+    server.createContext(
+        "/hello",
+        exchange -> {
+          final byte[] body = "hello".getBytes(StandardCharsets.UTF_8);
+          exchange.sendResponseHeaders(200, body.length);
+          try (OutputStream out = exchange.getResponseBody()) {
+            out.write(body);
+          }
+        });
+    server.start();
+    Files.write(
+        Paths.get(args[0]),
+        String.valueOf(server.getAddress().getPort()).getBytes(StandardCharsets.UTF_8));
+  }
+}

sentry-opentelemetry/sentry-opentelemetry-agent/src/test/kotlin/io/sentry/opentelemetry/agent/AgentSmokeTest.kt

@@ -0,0 +1,88 @@
+package io.sentry.opentelemetry.agent
+
+import com.google.common.truth.Truth.assertThat
+import io.sentry.opentelemetry.agent.fixture.HelloServer
+import io.sentry.test.MockSentryServer
+import io.sentry.test.transaction
+import io.sentry.time.Deadline
+import io.sentry.time.JavaMonotonicTicker
+import java.io.File
+import java.net.URL
+import java.nio.file.Files
+import java.util.concurrent.TimeUnit
+import kotlin.test.AfterTest
+import kotlin.test.Test
+
+/**
+ * Runs an app with the built agent attached, in a child JVM, so the test's own JVM stays
+ * uninstrumented. Instrumenting it would turn the test's HTTP calls and [MockSentryServer] itself
+ * into spans.
+ */
+class AgentSmokeTest {
+  private val server = MockSentryServer()
+  private val workDir = Files.createTempDirectory("agent-smoke-test").toFile()
+  private val appLog = File(workDir, "app.log")
+  private var app: Process? = null
+
+  @AfterTest
+  fun teardown() {
+    app?.destroyForcibly()?.waitFor()
+    server.close()
+    if (appLog.exists()) {
+      println(appLog.readText())
+    }
+    workDir.deleteRecursively()
+  }
+
+  @Test
+  fun `agent sends a transaction for an incoming request`() {
+    val port = launchWithAgent(HelloServer::class.java)
+
+    URL("http://127.0.0.1:$port/hello").readText()
+
+    // The agent's BatchSpanProcessor exports every 5s.
+    val envelope =
+      server.awaitEnvelope(timeoutMillis = 30_000) {
+        it.transaction()?.contexts?.trace?.operation == "http.server"
+      }
+    assertThat(envelope.header.sdkVersion!!.name).isEqualTo("sentry.java.opentelemetry.agent")
+  }
+
+  private fun launchWithAgent(mainClass: Class<*>): Int {
+    val portFile = File(workDir, "port")
+    val process =
+      ProcessBuilder(
+          File(System.getProperty("java.home"), "bin/java").path,
+          "-javaagent:${System.getProperty("sentry.test.agentJar")}",
+          "-cp",
+          File(mainClass.protectionDomain.codeSource.location.toURI()).path,
+          mainClass.name,
+          portFile.path,
+        )
+        .redirectErrorStream(true)
+        .redirectOutput(appLog)
+        .apply {
+          environment()["SENTRY_DSN"] = server.dsn
+          environment()["SENTRY_TRACES_SAMPLE_RATE"] = "1.0"
+          environment()["OTEL_TRACES_EXPORTER"] = "none"
+          environment()["OTEL_METRICS_EXPORTER"] = "none"
+          environment()["OTEL_LOGS_EXPORTER"] = "none"
+        }
+        .start()
+    app = process
+
+    val deadline = Deadline.after(JavaMonotonicTicker.getInstance(), 60, TimeUnit.SECONDS)
+    while (true) {
+      portFile
+        .takeIf { it.exists() }
+        ?.readText()
+        ?.toIntOrNull()
+        ?.let {
+          return it
+        }
+      check(process.isAlive) { "App exited with ${process.exitValue()}" }
+      check(!deadline.hasPassed()) { "App did not start within 60s" }
+      Thread.sleep(100)
+    }
+  }
+}