tictactoe: added hard AI

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

@@ -0,0 +1,22 @@
+package de.tims.tictactoe.ai;
+
+import de.tims.tictactoe.GameLogic;
+
+public class AIHard implements TicTacToeAI {
+	private static final char AI_CHAR = 'o';
+	private static final char EMPTY_CHAR = '-';
+	
+	private GameLogic gl;
+	
+	public AIHard(GameLogic gl) throws IllegalArgumentException {
+		if (gl.getBoard().length != 3) {
+			throw new IllegalArgumentException("Hard AI only supports 3x3 boards!");
+		}
+		this.gl = gl;
+	}
+
+	@Override
+	public void calculateNextMove() {
+		gl.setField(1, 1, AI_CHAR);
+	}
+}

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

@@ -0,0 +1,30 @@
+package de.tims.tictactoe.ai;
+
+import static org.mockito.Mockito.*;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import de.tims.tictactoe.GameLogic;
+
+@ExtendWith(MockitoExtension.class)
+class AIHardTest {
+	static int size = 3;
+	
+	@Mock
+	private GameLogic gl;
+	
+	@Test
+	void emptyBoardChooseMiddleField() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'-', '-', '-'}, {'-', '-', '-'}, {'-', '-', '-'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIHard(gl);
+		ai.calculateNextMove();
+		
+		verify(gl, times(1)).setField(1, 1, realChar);
+	}
+
+}