chore: unit tests for column change calculations

portion of #5

src/ui/render/test.rs

@@ -25,3 +25,25 @@ fn test_viewport_get_visible_rows() {
     assert_eq!(17 - (height - 2), *rows.first().expect("Failed to get first row"));
     assert_eq!(17, *rows.last().expect("Failed to get last row"));
 }
+
+#[test]
+fn test_viewport_visible_columns_after_length_change() {
+    let mut state = ViewportState::default();
+    let mut book = Book::new(Model::new_empty("test", "en", "America/New_York").expect("Failed to make model"));
+    let default_size = book.get_col_size(1).expect("Failed to get column size");
+    let width = dbg!(dbg!(default_size) * 12 / 2);
+    {
+        let viewport = Viewport::new(&book).with_selected(Address { row: 1, col: 17 });
+        let cols = viewport.get_visible_columns((width + 5) as u16, &mut state).expect("Failed to get visible columns");
+        assert_eq!(5, cols.len());
+        assert_eq!(17, cols.last().expect("Failed to get last column").idx);
+    }
+
+    book.set_col_size(1, default_size * 6).expect("Failed to set column size");
+    {
+        let viewport = Viewport::new(&book).with_selected(Address { row: 1, col: 1 });
+        let cols = viewport.get_visible_columns((width + 5) as u16, &mut state).expect("Failed to get visible columns");
+        assert_eq!(1, cols.len());
+        assert_eq!(1, cols.last().expect("Failed to get last column").idx);
+    }
+}