tictactoe: hard AI chooses edge field if field in the middle was already set

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

@@ -17,6 +17,17 @@ public class AIHard implements TicTacToeAI {
 
 	@Override
 	public void calculateNextMove() {
-		gl.setField(1, 1, AI_CHAR);
+		boolean emptyBoard = true;
+		char[][] board = gl.getBoard();
+		for (char[] row : board) {
+			for (char field : row) {
+				emptyBoard &= field == '-';
+			}
+		}
+		if (emptyBoard) {			
+			gl.setField(1, 1, AI_CHAR);
+		} else {
+			gl.setField(0, 0, AI_CHAR);
+		}
 	}
 }

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

@@ -26,5 +26,16 @@ class AIHardTest {
 		
 		verify(gl, times(1)).setField(1, 1, realChar);
 	}
+	
+	@Test
+	void middleFieldAlreadySetChooseEdgeField() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'-', '-', '-'}, {'-', 'x', '-'}, {'-', '-', '-'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIHard(gl);
+		ai.calculateNextMove();
+		
+		verify(gl, times(1)).setField(0, 0, realChar);
+	}
 
 }