tictactoe: AIEasy never sets a field which was already set

src/main/java/de/tims/tictactoe/ai/AIEasy.java

@@ -6,6 +6,7 @@ import java.util.Random;
 
 public class AIEasy implements TicTacToeAI {
 	private static final char AI_CHAR = 'o';
+	private static final char EMPTY_CHAR = '-';
 	
 	private Random rand;
 	private GameLogic gl;
@@ -14,14 +15,19 @@ public class AIEasy implements TicTacToeAI {
 	public AIEasy(GameLogic gl) {
 		this.gl = gl;
 		boardSize = gl.getBoard().length;
-		rand = new Random(gl.getBoard().hashCode());
+		rand = new Random();
 	}
 	
 	@Override
 	public void calculateNextMove() {
 		char[][] board = gl.getBoard();
-		int row = rand.nextInt(boardSize);
-		int col = rand.nextInt(boardSize);
+		int row;
+		int col;
+		do {
+			row = rand.nextInt(boardSize);
+			col = rand.nextInt(boardSize);
+		} while (board[row][col] != '-');
+			
 		gl.setField(row, col, AI_CHAR);
 	}
 	

src/test/java/de/tims/tictactoe/ai/AIEasyTest.java

@@ -32,6 +32,27 @@ class AIEasyTest {
 		verify(gl, times(100)).setField(intThat(new ChooseRandomFieldMatcher()), intThat(new ChooseRandomFieldMatcher()), eq(realChar));
 	}
 	
+	@Test
+	void notEmptyBoardChooseRandomFreeField() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'x', '-', 'o'}, {'-', 'o', '-'}, {'-', 'x', 'x'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIEasy(gl);
+		
+		//run method 100 times, because of random generator
+		for (int i = 0; i < 100; i++) {
+			ai.calculateNextMove();
+		}
+			
+		verify(gl, times(100)).setField(intThat(new ChooseRandomFieldMatcher()), intThat(new ChooseRandomFieldMatcher()), eq(realChar));
+		//verify that the method is never called with a field which was already set
+		verify(gl, never()).setField(0, 0, realChar);
+		verify(gl, never()).setField(0, 2, realChar);
+		verify(gl, never()).setField(1, 1, realChar);
+		verify(gl, never()).setField(2, 1, realChar);
+		verify(gl, never()).setField(2, 2, realChar);
+	}
+	
 	private static class ChooseRandomFieldMatcher implements ArgumentMatcher<Integer> {
 		@Override
 		public boolean matches(Integer argument) {