add test

Author: zeitlinger

instrumentation/spring/spring-boot-autoconfigure/src/main/java/io/opentelemetry/instrumentation/spring/autoconfigure/OpenTelemetryAutoConfiguration.java

@@ -5,6 +5,7 @@
 
 package io.opentelemetry.instrumentation.spring.autoconfigure;
 
+import io.opentelemetry.api.GlobalOpenTelemetry;
 import io.opentelemetry.api.OpenTelemetry;
 import io.opentelemetry.api.trace.TracerProvider;
 import io.opentelemetry.instrumentation.api.incubator.config.internal.InstrumentationConfig;
@@ -161,6 +162,9 @@ public OpenTelemetry openTelemetry(
             DeclarativeConfiguration.create(
                 model, new OpenTelemetrySdkComponentLoader(applicationContext));
         Runtime.getRuntime().addShutdownHook(new Thread(sdk::close));
+        // todo there is no equivalent to https://github.com/open-telemetry/opentelemetry-java/blob/7655192df504d28da2d2013f2fc49ec44ef6202e/sdk-extensions/autoconfigure/src/main/java/io/opentelemetry/sdk/autoconfigure/LoggerProviderConfiguration.java#L96
+        // so we get a NPE when there is no global OpenTelemetry instance set
+        GlobalOpenTelemetry.set(sdk);
         logStart();
         return sdk;
       }