test: improve utils coverage (#4230)

* test: improve utils coverage

* refactor: review - rename isDefined to isNonNullable, update tests and return statement

packages/twenty-front/src/utils/array/groupArrayItemsBy.ts

@@ -1,8 +1,30 @@
-export const groupArrayItemsBy = <Item, Key extends string>(
-  array: Item[],
-  computeGroupKey: (item: Item) => Key,
+/**
+ * Groups an array of items by a key computed from each item.
+ *
+ * @param array - The array to group.
+ * @param computeGroupKey - A function that computes the group key to which the item belongs.
+ *
+ * @returns An object with items grouped by a computed key.
+ *
+ * @example
+ * groupArrayItemsBy(
+ *   [{ id: '1', type: 'fruit' }, { id: '2', type: 'vegetable' }, { id: '3', type: 'fruit' }],
+ *   ({ type }) => type,
+ * )
+ * ⬇️
+ * {
+ *   fruit: [{ id: '1', type: 'fruit' }, { id: '3', type: 'fruit' }],
+ *   vegetable: [{ id: '2', type: 'vegetable' }],
+ * }
+ */
+export const groupArrayItemsBy = <
+  ArrayItem extends Record<string, unknown>,
+  Key extends string,
+>(
+  array: ArrayItem[],
+  computeGroupKey: (item: ArrayItem) => Key,
 ) =>
-  array.reduce<Partial<Record<Key, Item[]>>>((result, item) => {
+  array.reduce<Partial<Record<Key, ArrayItem[]>>>((result, item) => {
     const groupKey = computeGroupKey(item);
     const previousGroup = result[groupKey] || [];