tictactoe: hard AI sets middle field if it hasnt been set yet

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

@@ -21,10 +21,10 @@ public class AIHard implements TicTacToeAI {
 		char[][] board = gl.getBoard();
 		for (char[] row : board) {
 			for (char field : row) {
-				emptyBoard &= field == '-';
+				emptyBoard &= field == EMPTY_CHAR;
 			}
 		}
-		if (emptyBoard) {			
+		if (emptyBoard || board[1][1] == EMPTY_CHAR) {			
 			gl.setField(1, 1, AI_CHAR);
 		} else {
 			gl.setField(0, 0, AI_CHAR);

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

@@ -38,4 +38,15 @@ class AIHardTest {
 		verify(gl, times(1)).setField(0, 0, realChar);
 	}
 	
+	@Test
+	void opponentDidntChooseMiddleFieldSoAIDoes() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'-', '-', 'x'}, {'-', '-', '-'}, {'-', '-', '-'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIHard(gl);
+		ai.calculateNextMove();
+		
+		verify(gl, times(1)).setField(1, 1, realChar);
+	}
+
 }