Update edge_cases function to handle isolated vertices and add a test for three connected vertices

Author: wifi:)

pgtap/ordering/kingOrdering/edge_cases.pg

@@ -20,7 +20,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 BEGIN;
 
 UPDATE edges SET cost = sign(cost), reverse_cost = sign(reverse_cost);
-SELECT CASE WHEN NOT min_version('4.0.0') THEN plan(1) ELSE plan(5) END;
+SELECT CASE WHEN NOT min_version('4.0.0') THEN plan(1) ELSE plan(6) END;
 
 
 CREATE OR REPLACE FUNCTION edge_cases()
@@ -97,7 +97,17 @@ FROM pgr_kingOrdering('SELECT id, source, target, cost, reverse_cost FROM isolat
 );
 
 RETURN QUERY
-SELECT set_eq('q5', $$VALUES (1, 1), (2, 2)$$, 'Showing both vertex of disconnected graph');
+SELECT set_eq('q5', $$VALUES (1, 1), (2, 2)$$, 'Both isolated vertices are returned for a disconnected graph');
+
+-- 3 vertices test
+
+PREPARE q6 AS
+SELECT *
+FROM pgr_kingOrdering('SELECT id, source, target, cost, reverse_cost FROM edges WHERE id <= 2'
+);
+
+RETURN QUERY
+SELECT set_eq('q6', $$VALUES (1, 5), (2, 6), (3, 10)$$, 'Three connected vertices are ordered as expected');
 
 END;
 $BODY$