Added test with runningDifference function. #2590

dbms/tests/queries/0_stateless/00653_running_difference.reference

+0
+1
+4
+5
+-
+0
+\N
+1
+\N
+7
+-
+\N
+0
+-
+\N
+\N
+0
+2
+\N
+\N
+2

dbms/tests/queries/0_stateless/00653_running_difference.sql

+select runningDifference(x) from (select arrayJoin([0, 1, 5, 10]) as x);
+select '-';
+select runningDifference(x) from (select arrayJoin([2, Null, 3, Null, 10]) as x);
+select '-';
+select runningDifference(x) from (select arrayJoin([Null, 1]) as x);
+select '-';
+select runningDifference(x) from (select arrayJoin([Null, Null, 1, 3, Null, Null, 5]) as x);
+