PBCKP-294 test add expect_error into safe_psql()

Author: v.shepard

testgres/node.py

@@ -894,7 +894,7 @@ def psql(self,
         return process.returncode, out, err
 
     @method_decorator(positional_args_hack(['dbname', 'query']))
-    def safe_psql(self, query=None, **kwargs):
+    def safe_psql(self, query=None, expect_error=False, **kwargs):
         """
         Execute a query using psql.
 
@@ -904,6 +904,8 @@ def safe_psql(self, query=None, **kwargs):
             dbname: database name to connect to.
             username: database user name.
             input: raw input to be passed.
+            expect_error: if True - fail if we didn't get ret
+                          if False - fail if we got ret
 
             **kwargs are passed to psql().
 
@@ -916,7 +918,12 @@ def safe_psql(self, query=None, **kwargs):
 
         ret, out, err = self.psql(query=query, **kwargs)
         if ret:
-            raise QueryException((err or b'').decode('utf-8'), query)
+            if expect_error:
+                out = (err or b'').decode('utf-8')
+            else:
+                raise QueryException((err or b'').decode('utf-8'), query)
+        elif expect_error:
+            assert False, f"Exception was expected, but query finished successfully: `{query}` "
 
         return out