add more permutations

src/test/regress/expected/isolation_reference_table.out

@@ -103,3 +103,37 @@ step s1-drop:
 step s2-commit:
     COMMIT;
 
+
+starting permutation: s2-create s2-begin s2-drop s1-create s2-commit
+create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+step s2-create:
+    CREATE TABLE reference_table_s2(a int);
+ 	SELECT create_reference_table('reference_table_s2');
+
+create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+step s2-begin:
+    BEGIN;
+
+step s2-drop:
+    DROP TABLE reference_table_s2;
+
+step s1-create:
+    CREATE TABLE reference_table_s1(a int);
+ 	SELECT create_reference_table('reference_table_s1');
+
+create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+step s2-commit:
+    COMMIT;
+

src/test/regress/spec/isolation_reference_table.spec

@@ -78,3 +78,4 @@ permutation "s1-create" "s2-create" "s1-begin" "s1-drop" "s2-drop" "s1-commit"
 
 // create and drop don't block each other
 permutation "s1-create" "s2-begin" "s2-create" "s1-drop" "s2-commit"
+permutation "s2-create" "s2-begin" "s2-drop" "s1-create" "s2-commit"