New implementation of hashCode() + test

Author: parubok

src/main/java/io/github/parubok/stream/TableCell.java

@@ -66,10 +66,7 @@ public int get(Field field) {
 
     @Override
     public int hashCode() {
-        int result = 17;
-        result = 37 * result + row;
-        result = 37 * result + col;
-        return result;
+        return Integer.hashCode(row + col);
     }
 
     @Override

src/test/java/io/github/parubok/stream/TableCellTest.java

@@ -224,4 +224,13 @@ public void get_field() {
         Assertions.assertEquals(10, c.get(TableCell.ROW));
         Assertions.assertEquals(2, c.get(TableCell.COLUMN));
     }
+
+    @Test
+    public void hashCode_() {
+        for (int i = 0; i < 100; i++) {
+            Assertions.assertEquals(new TableCell(i, i).hashCode(), new TableCell(i, i).hashCode());
+            Assertions.assertEquals(new TableCell(0, i).hashCode(), new TableCell(0, i).hashCode());
+            Assertions.assertEquals(new TableCell(i, 0).hashCode(), new TableCell(i, 0).hashCode());
+        }
+    }
 }