Recursion limit for bailing on unsolvable, more extensive testing and additions to interface

app/src/test/java/sudoku/SolverTest.java

@@ -1,6 +1,6 @@
 package sudoku;
 
-import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.RepeatedTest;
 import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.*;
 import java.util.stream.IntStream;
@@ -45,6 +45,7 @@ class SolverTest {
     }
 
     @Test
+    @RepeatedTest(100)
     void solverTest() {
         Solver solver = new Solver();
         assertFalse(solver.isSolved());
@@ -52,12 +53,16 @@ class SolverTest {
         assertTrue(solver.isSolved());
 
         solver.clear();
-        solver.randomizeBoard();
         assertFalse(solver.isSolved());
         assertTrue(solver.solve());
-        solver.clear();
+    }
+
+    @Test
+    @RepeatedTest(100)
+    void randomizeBoardGuaranteeSolvableTest() {
+        Solver solver = new Solver();
         solver.randomizeBoard();
-        assertFalse(solver.isSolved());
+        assertTrue(solver.solve());
     }
 
     @Test
@@ -79,11 +84,26 @@ class SolverTest {
     }
 
     @Test
-    @Disabled
     void unsolvableTest() {
         Solver solver = new Solver();
+        
+        // Simple example
+        solver.clear();
         solver.set(0, 0, 1);
         solver.set(0, 1, 1);
         assertFalse(solver.solve());
+
+        // More complex example
+        solver.clear();
+        solver.set(0, 5, 7);
+        solver.set(0, 6, 8);
+        solver.set(0, 7, 2);
+        solver.set(1, 5, 3);
+        solver.set(2, 7, 1);
+        solver.set(3, 1, 4);
+        solver.set(5, 2, 8);
+        solver.set(5, 8, 6);
+        solver.set(7, 1, 8);
+        assertFalse(solver.solve());
     }
 }