Improve complex_numbers tests

Now these tests actually test results properly.

exercises/complex-numbers/complex_numbers_tests.plt

@@ -124,16 +124,16 @@ pending :-
 
 :- begin_tests(exponent).
 
-    test(eulers_identity, condition(pending)) :-
-        exponent((0,pi), (X,Y)), X \= -1, Y \= 0.
+    test(eulers_identity, condition(true)) :-
+        exponent((0,pi), (X,Y)), X > -1.001, X < -0.999, Y > -0.001, Y< 0.001.
 
-    test(exponential_of_zero, condition(pending)) :-
-        exponent((0,0), (X,Y)), X \= 1, Y \= 0.
+    test(exponential_of_zero, condition(true)) :-
+        exponent((0,0), (X,Y)), X > 0.999, X < 1.001, Y > -0.001, Y < 0.001.
 
-    test(exponential_of_purely_real_number, condition(pending)) :-
-        exponent((1,0), (X,Y)), X \= e, Y \= 0.
+    test(exponential_of_purely_real_number, condition(true)) :-
+        exponent((1,0), (X,Y)), X > e - 0.001, X < e + 0.001, Y > -0.001, Y < 0.001.
 
-    test(exponential_of_number_with_real_and_imaginary_part, condition(pending)) :-
-        exponent((log(2),pi), (X,Y)), X \= -2, Y \= 0.
+    test(exponential_of_number_with_real_and_imaginary_part, condition(true)) :-
+        exponent((log(2),pi), (X,Y)), X > -2.001, X < -1.999, Y > -0.001, Y < 0.001.
 
 :- end_tests(exponent).