TS-45056 Rework

Author: stahlbauer

agent/src/test/java/com/teamscale/jacoco/agent/PreMainTest.java

@@ -2,9 +2,15 @@
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 
+import java.io.IOException;
 import java.lang.instrument.Instrumentation;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
 
 /**
@@ -45,4 +51,46 @@ void premainDoesNotThrowOnConfigIdWithoutCredentials() {
 		assertThatCode(() -> PreMain.premain("config-id=some-config", null))
 				.doesNotThrowAnyException();
 	}
+
+	/**
+	 * Exercises the top-level {@code try}/{@code catch} in {@link PreMain#premain(String, Instrumentation)} that routes
+	 * into {@code logStartupFailure} — the safety net for failures that surface <em>after</em> options have been parsed
+	 * (and are therefore not covered by the {@code AgentOption*Exception} catches inside {@code startProfiler}).
+	 * <p>
+	 * The trick: valid options pass parsing, then a {@code null} {@link Instrumentation} forces JaCoCo's runtime setup
+	 * to dereference {@code null} (first at {@code AgentModule.openPackage(inst, …)} inside
+	 * {@code JaCoCoPreMain.createRuntime}). The resulting {@link NullPointerException} is a stand-in for real-world
+	 * post-parse failures — e.g. a Jetty {@code BindException} when {@code http-server-port} is taken, or an
+	 * {@code UploaderException} during uploader construction — which would bubble up the same way. In production the
+	 * JVM always supplies a non-null {@code Instrumentation}; passing {@code null} here is only a cheap way to stage
+	 * the failure without a running JVM agent attach.
+	 * <p>
+	 * A custom {@code logging-config} points logback at a file inside {@code tempDir} so we can read back the emitted
+	 * error event. A plain {@link ch.qos.logback.core.read.ListAppender} attached in the test would be detached again
+	 * by the {@code LoggerContext.reset()} that {@code LoggingUtils.reconfigureLoggerContext} performs during option
+	 * parsing.
+	 */
+	@Test
+	void premainLogsFailureWhenJaCoCoSetupThrows(@TempDir Path tempDir) throws IOException {
+		Path logFile = tempDir.resolve("agent.log");
+		Path logbackConfig = tempDir.resolve("logback.xml");
+		Files.write(logbackConfig, ("<configuration>\n"
+				+ "  <appender name=\"FILE\" class=\"ch.qos.logback.core.FileAppender\">\n"
+				+ "    <file>" + logFile.toAbsolutePath() + "</file>\n"
+				+ "    <encoder><pattern>%-5level %logger - %msg%n%ex</pattern></encoder>\n"
+				+ "  </appender>\n"
+				+ "  <root level=\"INFO\"><appender-ref ref=\"FILE\"/></root>\n"
+				+ "</configuration>\n").getBytes(StandardCharsets.UTF_8));
+
+		assertThatCode(() -> PreMain.premain(
+				"logging-config=" + logbackConfig.toAbsolutePath() + ",includes=com.example.*", null))
+				.doesNotThrowAnyException();
+
+		assertThat(logFile).exists();
+		String log = new String(Files.readAllBytes(logFile), StandardCharsets.UTF_8);
+		assertThat(log)
+				.contains("ERROR")
+				.contains("failed to start up")
+				.contains("NullPointerException");
+	}
 }