diff --git a/src/test/c/test_TicTacToe.c b/src/test/c/test_TicTacToe.c
index f0d5ab7..0dc4844 100644
--- a/src/test/c/test_TicTacToe.c
+++ b/src/test/c/test_TicTacToe.c
@@ -104,6 +104,22 @@ void test_TicTacToe_Winner_O_col_3(void)
     /* act */
     actual = Winner(board);
 
+    /* assert */
+    TEST_ASSERT_EQUAL_INT(expected, actual);
+}
+void test_TicTacToe_Winner_X_diagonal_1(void)
+{
+    /* arrange */
+    int expected = 1;
+    int actual;
+    char board[3][3] = {
+        {'X', 'O', 'X'},
+        {'O', 'X', 'O'},
+        {'O', '_', 'X'}
+    };
+    /* act */
+    actual = Winner(board);
+
     /* assert */
     TEST_ASSERT_EQUAL_INT(expected, actual);
 }
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