test: fix failing test cases

Author: olavloite

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionClient.java

@@ -241,7 +241,6 @@ SessionImpl createSession() {
     XGoogSpannerRequestId reqId = nextRequestId(channelId, 1);
     ISpan span = spanner.getTracer().spanBuilder(SpannerImpl.CREATE_SESSION, this.commonAttributes);
     try (IScope s = spanner.getTracer().withSpan(span)) {
-      XGoogSpannerRequestId reqId = this.nextRequestId(channelId, 1);
       com.google.spanner.v1.Session session =
           spanner
               .getRpc()

google-cloud-spanner/src/main/java/com/google/cloud/spanner/XGoogSpannerRequestId.java

@@ -160,7 +160,7 @@ public XGoogSpannerRequestId nextRequestId(long channelId, int attempt) {
     }
   }
 
-  public static void assertMonotonicityOfIds(String prefix, List<XGoogSpannerRequestId> reqIds) {
+  static void assertMonotonicityOfIds(String prefix, List<XGoogSpannerRequestId> reqIds) {
     int size = reqIds.size();
 
     List<String> violations = new ArrayList<>();
@@ -172,7 +172,7 @@ public static void assertMonotonicityOfIds(String prefix, List<XGoogSpannerReque
       }
     }
 
-    if (violations.size() == 0) {
+    if (violations.isEmpty()) {
       return;
     }