Add test. Address other PR concerns

dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/AgentInstaller.java

@@ -80,7 +80,8 @@ public class AgentInstaller {
                                     "datadog.trace.bootstrap.instrumentation.java.concurrent.RunnableWrapper")
                                 .or(
                                     named(
-                                        "datadog.trace.bootstrap.instrumentation.java.concurrent.CallableWrapper")))))
+                                            "datadog.trace.bootstrap.instrumentation.java.concurrent.CallableWrapper")
+                                        .or(nameStartsWith("datadog.trace.agent.test"))))))
             .or(nameStartsWith("datadog.opentracing."))
             .or(nameStartsWith("datadog.slf4j."))
             .or(nameStartsWith("net.bytebuddy."))
@@ -142,7 +143,7 @@ public class AgentInstaller {
       try {
         agentBuilder = instrumenter.instrument(agentBuilder);
         numInstrumenters++;
-      } catch (final Throwable e) {
+      } catch (final Exception | LinkageError e) {
         log.error("Unable to load instrumentation {}", instrumenter.getClass().getName(), e);
       }
     }

dd-java-agent/agent-tooling/src/test/groovy/datadog/trace/agent/tooling/AgentInstallerTest.groovy

@@ -0,0 +1,18 @@
+package datadog.trace.agent.tooling
+
+import datadog.trace.agent.test.AgentTestRunner
+import datadog.trace.agent.test.TestClass
+
+class AgentInstallerTest extends AgentTestRunner {
+
+  def "Exception in instrumentation is limited to that instrumentation"() {
+    given:
+    TestClass instance = new TestClass()
+
+    when:
+    String returnValue = instance.doSomething()
+
+    then:
+    returnValue == "overridden value"
+  }
+}

dd-java-agent/agent-tooling/src/test/java/datadog/trace/agent/test/BadInstrumentation.java

@@ -0,0 +1,26 @@
+package datadog.trace.agent.test;
+
+import com.google.auto.service.AutoService;
+import datadog.trace.agent.tooling.Instrumenter;
+import java.util.Collections;
+import java.util.Map;
+import net.bytebuddy.description.method.MethodDescription;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.matcher.ElementMatcher;
+
+@AutoService(Instrumenter.class)
+public class BadInstrumentation extends Instrumenter.Default {
+  public BadInstrumentation() {
+    super("bad-test-instrumentation");
+  }
+
+  @Override
+  public ElementMatcher<? super TypeDescription> typeMatcher() {
+    throw new RuntimeException("Test Exception");
+  }
+
+  @Override
+  public Map<? extends ElementMatcher<? super MethodDescription>, String> transformers() {
+    return Collections.emptyMap();
+  }
+}

dd-java-agent/agent-tooling/src/test/java/datadog/trace/agent/test/GoodInstrumentation.java

@@ -0,0 +1,37 @@
+package datadog.trace.agent.test;
+
+import static java.util.Collections.singletonMap;
+import static net.bytebuddy.matcher.ElementMatchers.named;
+
+import com.google.auto.service.AutoService;
+import datadog.trace.agent.tooling.Instrumenter;
+import java.util.Map;
+import net.bytebuddy.asm.Advice;
+import net.bytebuddy.description.method.MethodDescription;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.matcher.ElementMatcher;
+
+@AutoService(Instrumenter.class)
+public class GoodInstrumentation extends Instrumenter.Default {
+
+  public GoodInstrumentation() {
+    super("good-test-instrumentation");
+  }
+
+  @Override
+  public ElementMatcher<? super TypeDescription> typeMatcher() {
+    return named(TestClass.class.getName());
+  }
+
+  @Override
+  public Map<? extends ElementMatcher<? super MethodDescription>, String> transformers() {
+    return singletonMap(named("doSomething"), GoodInstrumentationAdvice.class.getName());
+  }
+
+  public static class GoodInstrumentationAdvice {
+    @Advice.OnMethodExit
+    public static void changeReturn(@Advice.Return(readOnly = false) String originalValue) {
+      originalValue = "overridden value";
+    }
+  }
+}

dd-java-agent/agent-tooling/src/test/java/datadog/trace/agent/test/TestClass.java

@@ -0,0 +1,7 @@
+package datadog.trace.agent.test;
+
+public class TestClass {
+  public String doSomething() {
+    return "original value";
+  }
+}