Add DonaldKnuthAlgorithm unit test

culminating-mastermind/app/src/test/java/mastermind/solvers/DonaldKnuthAlgorithmTest.java

@@ -0,0 +1,46 @@
+package mastermind.solvers;
+
+import mastermind.core.Code;
+import mastermind.core.Response;
+import mastermind.core.solvers.DonaldKnuthAlgorithm;
+import mastermind.core.solvers.MastermindSolver;
+import mastermind.utils.Tuple2;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+class DonaldKnuthAlgorithmTest {
+    @Test
+    void testFirstGuess() {
+        final DonaldKnuthAlgorithm solver = new DonaldKnuthAlgorithm();
+        final Code firstGuess = solver.guess();
+        final Code expectedFirstGuess = new Code(List.of(0, 0, 1, 1));
+
+        assertEquals(expectedFirstGuess.getColors(), firstGuess.getColors());
+    }
+
+    @Test
+    void testGuesses() {
+        // Secret code is purple yellow blue red
+        final Code secretCode = new Code(List.of(5, 3, 2, 1));
+        final DonaldKnuthAlgorithm solver = new DonaldKnuthAlgorithm();
+
+        Tuple2<MastermindSolver.Status, Code> result = new Tuple2<>(MastermindSolver.Status.Continue, solver.guess());
+
+        while (result.first == MastermindSolver.Status.Continue) {
+            final Response hints = new Response(secretCode, result.second);
+            result = solver.guess(hints);
+        }
+
+        if (result.first == MastermindSolver.Status.Lose) {
+            fail("Donald Knuth algorithm failed to solve the secret code");
+        }
+
+        assertTrue(solver.getAttempts() <= 6);
+    }
+}