test: add tests for toNextSelectedYear with minor improvements

src/tests/year-grid/to-next-selected-year.test.ts

@@ -0,0 +1,99 @@
+import { expect } from '@open-wc/testing';
+
+import { toNextSelectedYear } from '../../year-grid/to-next-selected-year';
+import type { ToNextSelectableYearInit } from '../../year-grid/typings';
+import { messageFormatter } from '../test-utils/message-formatter';
+
+describe(toNextSelectedYear.name, () => {
+  const defaultInit: ToNextSelectableYearInit = {
+    key: 'ArrowUp',
+    max: new Date('2021-01-01'),
+    min: new Date('2019-01-01'),
+    year: 2020,
+  };
+  const defaultInitWithGrid: ToNextSelectableYearInit = {
+    key: 'ArrowUp',
+    max: new Date('2032-01-01'),
+    min: new Date('2017-01-01'),
+    year: 2022,
+  };
+
+  type A = [Partial<ToNextSelectableYearInit>, number];
+  const cases: A[] = [
+    // cap at min or max
+    [
+      {},
+      defaultInit.min.getUTCFullYear(),
+    ],
+    [
+      { key: 'ArrowDown' },
+      defaultInit.max.getUTCFullYear(),
+    ],
+    [
+      { key: 'ArrowLeft' },
+      defaultInit.min.getUTCFullYear(),
+    ],
+    [
+      { key: 'ArrowRight' },
+      defaultInit.max.getUTCFullYear(),
+    ],
+    [
+      { key: 'End' },
+      defaultInit.max.getUTCFullYear(),
+    ],
+    [
+      { key: 'Home' },
+      defaultInit.min.getUTCFullYear(),
+    ],
+    [
+      { key: ' ' },
+      defaultInit.year,
+    ],
+
+    // within min and max
+    [
+      { ...defaultInitWithGrid },
+      defaultInitWithGrid.year - 4,
+    ],
+    [
+      { ...defaultInitWithGrid, key: 'ArrowDown' },
+      defaultInitWithGrid.year + 4,
+    ],
+    [
+      { ...defaultInitWithGrid, key: 'ArrowLeft' },
+      defaultInitWithGrid.year - 1,
+    ],
+    [
+      { ...defaultInitWithGrid, key: 'ArrowRight' },
+      defaultInitWithGrid.year + 1,
+    ],
+    [
+      { ...defaultInitWithGrid, key: 'End' },
+      defaultInitWithGrid.max.getUTCFullYear(),
+    ],
+    [
+      { ...defaultInitWithGrid, key: 'Home' },
+      defaultInitWithGrid.min.getUTCFullYear(),
+    ],
+    [
+      { ...defaultInitWithGrid, key: ' ' },
+      defaultInitWithGrid.year,
+    ],
+  ];
+
+  cases.forEach(a => {
+    const [testPartialInit, expected] = a;
+
+    it(
+      messageFormatter('returns next selected year (init=%j)', a),
+      () => {
+        const result = toNextSelectedYear({
+          ...defaultInit,
+          ...testPartialInit,
+        });
+
+        expect(result).equal(expected);
+      }
+    );
+  });
+});

src/year-grid-button/app-year-grid-button.ts

@@ -1,11 +1,11 @@
-import { customElement } from 'lit/decorators/custom-element.js';
+import { customElement } from 'lit/decorators.js';
 
 import { APP_YEAR_GRID_BUTTON_NAME } from './constants.js';
 import { YearGridButton } from './year-grid-button.js';
 
 
 @customElement(APP_YEAR_GRID_BUTTON_NAME)
-class AppYearGridButton extends YearGridButton {}
+export class AppYearGridButton extends YearGridButton {}
 
 declare global {
   interface HTMLElementTagNameMap {

src/year-grid/app-year-grid.ts

@@ -4,7 +4,7 @@ import { APP_YEAR_GRID_NAME } from './constants.js';
 import { YearGrid } from './year-grid.js';
 
 @customElement(APP_YEAR_GRID_NAME)
-class AppYearGrid extends YearGrid {}
+export class AppYearGrid extends YearGrid {}
 
 declare global {
   interface HTMLElementTagNameMap {

src/year-grid/ to-next-selected-year.ts → src/year-grid/to-next-selected-year.ts

@@ -7,14 +7,33 @@ export function toNextSelectedYear({
   min,
   year,
 }: ToNextSelectableYearInit): number {
+  let newYear = year;
+
   switch (key) {
-    case keyArrowUp: return year - 4;
-    case keyArrowDown: return year + 4;
-    case keyArrowLeft: return year - 1;
-    case keyArrowRight: return year  + 1;
+    case keyArrowUp: {
+      newYear = year - 4;
+      break;
+    }
+    case keyArrowDown: {
+      newYear = year + 4;
+      break;
+    }
+    case keyArrowLeft: {
+      newYear = year - 1;
+      break;
+    }
+    case keyArrowRight: {
+      newYear = year + 1;
+      break;
+    }
     case keyEnd: return max.getUTCFullYear();
     case keyHome: return min.getUTCFullYear();
     default:
       return year;
   }
+
+  return Math.min(
+    Math.max(min.getUTCFullYear(), newYear),
+    max.getUTCFullYear()
+  );
 }