test: add tests for splitString

src/helpers/split-string.ts

@@ -1,25 +1,23 @@
 type SplitStringCallbackFn<ReturnType> = (
-  element: ReturnType,
+  element: string,
   index: number,
-  array: ReturnType[]
+  array: string[]
 ) => ReturnType;
 
-export type splitString = {
-  (source: string): string[];
-  <ReturnType>(source: string, callbackFn: SplitStringCallbackFn<ReturnType>): ReturnType[];
-}
-
-export function splitString<SourceType extends string = string, ReturnType = string>(
-  source: SourceType,
-  callbackFn?: SplitStringCallbackFn<ReturnType>,
+export function splitString<ReturnType = string>(
+  source: string,
+  splitFunction?: SplitStringCallbackFn<ReturnType>,
   separator: RegExp | string = /,\s*/
 ): ReturnType[] {
   const dateList = typeof source === 'string' && source.length > 0
-    ? source.split(separator) as unknown as ReturnType[]
+    ? source.split(separator)
     : [];
 
   if (!dateList.length) return [];
-  if (callbackFn == null) return dateList;
+  if (splitFunction == null) return dateList as unknown as ReturnType[];
 
-  return dateList.map(callbackFn);
+  return dateList.map(
+    (n, i, arr) =>
+      splitFunction(n, i, arr)
+  );
 }

src/tests/helpers/split-string.test.ts

@@ -0,0 +1,53 @@
+import { expect } from '@open-wc/testing';
+
+import { splitString } from '../../helpers/split-string';
+import { messageFormatter } from '../test-utils/message-formatter';
+
+describe(splitString.name, () => {
+  const str = 'hello, world, everyone';
+  const expected = str.split(/,\s*/);
+
+  type A = [string, string[]];
+
+  const cases: A[] = [
+    ['', []],
+    [str, expected],
+  ];
+
+  cases.forEach((a) => {
+    it(
+      messageFormatter('splits string (%s)', a),
+      () => {
+        const [testSource, expected] = a;
+        const result = splitString(testSource);
+
+        expect(result).deep.equal(expected);
+      }
+    );
+  });
+
+  type A1 = [RegExp?];
+
+  const cases1: A1[] = [
+    [],
+    [/,\s/],
+  ];
+
+  cases1.forEach((a) => {
+    it(
+      messageFormatter('splits string with optional callback and optional separator (%s)', a),
+      () => {
+        const [testSeparator] = a;
+
+        const result = splitString<[string]>(
+          str,
+          (n) => [n],
+          testSeparator
+        );
+
+        expect(result).deep.equal(expected.map(n => [n]));
+      }
+    );
+  });
+
+});