test: add Array2DUtil test

src/test/java/com/adventofcode/flashk/common/Array2DUtilTest.java

@@ -0,0 +1,27 @@
+package com.adventofcode.flashk.common;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class Array2DUtilTest {
+
+    @Test
+    void transposeTest() {
+        char[][] array = {
+                {'a', 'b', 'c'},
+                {'d', 'e', 'f'},
+                {'g', 'h', 'i'}
+        };
+
+        char[][] expected = {
+                {'a', 'd', 'g'},
+                {'b', 'e', 'h'},
+                {'c', 'f', 'i'}
+        };
+
+        char[][] actual = Array2DUtil.transpose(array);
+
+        assertArrayEquals(expected, actual);
+    }
+}