adding a test prefix to db to allow for concurrent runs (#867)

Author: jabubake

spanner/cloud-client/src/test/java/com/example/spanner/SpannerSampleIT.java

@@ -25,6 +25,7 @@
 
 import java.io.ByteArrayOutputStream;
 import java.io.PrintStream;
+import java.util.UUID;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -39,7 +40,7 @@
 public class SpannerSampleIT {
   // The instance needs to exist for tests to pass.
   private final String instanceId = System.getProperty("spanner.test.instance");
-  private final String databaseId = System.getProperty("spanner.sample.database");
+  private final String databaseId = formatForTest(System.getProperty("spanner.sample.database"));
   DatabaseId dbId;
   DatabaseAdminClient dbClient;
   private long lastUpdateDataTimeInMillis;
@@ -116,4 +117,8 @@ public void testSample() throws Exception {
     out = runSample("readonlytransaction");
     assertThat(out.replaceAll("[\r\n]+", " ")).containsMatch("(Total Junk.*){2}");
   }
+
+  private String formatForTest(String name) {
+    return name + "-" + UUID.randomUUID().toString().substring(0, 20);
+  }
 }