[NO ISSUE][SQLPP] Improve error message for unsupported EXPLAIN

- user model changes: no
- storage format changes: no
- interface changes: no

Details:
- Improve error message raised when EXPLAIN
  is not supported for a given statement

Change-Id: Idd7844ca3d9e3c2c0de0b070e4a76282cb96e278
Reviewed-on: https://asterix-gerrit.ics.uci.edu/3420
Sonar-Qube: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Dmitry Lychagin <dmitry.lychagin@couchbase.com>
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
index d1098dc..112277c 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_sqlpp.xml
@@ -174,6 +174,14 @@
         <output-dir compare="Text">explain_field_access_closed</output-dir>
       </compilation-unit>
     </test-case>
+    <test-case FilePath="explain">
+      <compilation-unit name="explain_negative">
+        <output-dir compare="Text">explain_simple</output-dir>
+        <expected-error>ASX1001: Syntax error: EXPLAIN is not supported for this kind of statement</expected-error>
+        <expected-error>ASX1001: Syntax error: EXPLAIN is not supported for this kind of statement</expected-error>
+        <expected-error>ASX1001: Syntax error: EXPLAIN is not supported for this kind of statement</expected-error>
+      </compilation-unit>
+    </test-case>
   </test-group>
   <test-case FilePath="flwor">
     <compilation-unit name="let33">