Working solution!

json_tests.py

@@ -33,13 +33,7 @@ class TaskTester(unittest.TestCase):
         in_prolog = FOL2prolog(self.in_preds)
         with open('prolog/input_example_1.pl', 'w') as file:
             file.write(in_prolog)
-        # with open('prolog/solution_1.pl', 'rt') as file:
-        #     prolog_program = file.read()
 
-        # full_program = in_prolog + prolog_program
-        #
-
-        # program = "[input_example_1].\n[solution_1].\n[background_knowledge].\n"
         program = "[input_example_1], [solution_1], [background_knowledge], print_results, halt."
 
         out_prolog = run_prolog_program(program=program, curr_dir='./prolog')
@@ -51,9 +45,6 @@ class TaskTester(unittest.TestCase):
         self.assertTrue((out_grid == self.output_grid).all())
 
 
-        print("done")
-
-
 
 if __name__ == '__main__':
     unittest.main()

prolog/background_knowledge.pl

+% Students must define row/1, column/1 and output_colour/3.
+
 output_with_default(Row, Column, Colour) :-
     row(Row),
     column(Column),
-    (output(Row, Column, Colour), Colour \= _) -> true;
-    Colour = black.
+    output_colour(Row, Column, Colour).
 
+output_with_default(Row, Column, black) :-
+    row(Row),
+    column(Column),
+    \+ output_colour(Row, Column, _).
 
 print_results([]).
 print_results([(R, C, Colour) | Rest]) :-
@@ -14,5 +19,5 @@ print_results([(R, C, Colour) | Rest]) :-
     print_results(Rest).
 
 print_results :-
-    setof((R, C, Colour), R^C^Colour^output_colour(R, C, Colour), Results),
+    setof((R, C, Colour), R^C^Colour^output_with_default(R, C, Colour), Results),
     print_results(Results).