Better test coverage of polyfills

dubzzz · Jul 3, 2018 · 7f50459 · 7f50459
1 parent 3d52506
commit 7f50459
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Showing 2 changed files with 74 additions and 27 deletions.
diff --git a/src/check/polyfills.ts b/src/check/polyfills.ts
@@ -1,43 +1,47 @@
 // All the implementations below are directly taken from https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference
 
 /** @hidden */
-export const ObjectEntries = (obj: any): [string, any][] => {
-  if (Object.entries) return Object.entries(obj);
+export const ObjectEntriesImpl = (obj: any): [string, any][] => {
   const ownProps = Object.keys(obj);
   let i = ownProps.length;
   const resArray = new Array(i);
   while (i--) resArray[i] = [ownProps[i], obj[ownProps[i]]];
   return resArray;
 };
 
-/** hidden */
-export const StringPadEnd = (src: string, targetLength: number, padString: string) => {
-  if (src && src.padEnd) return src.padEnd(targetLength, padString);
+/** @hidden */
+export const ObjectEntries = Object.entries ? Object.entries : ObjectEntriesImpl;
+
+/** @hidden */
+const repeatUpToLength = (src: string, targetLength: number): string => {
+  for (; targetLength > src.length; src += src);
+  return src;
+};
+
+/** @hidden */
+export const StringPadEndImpl = (src: string, targetLength: number, padString: string) => {
   targetLength = targetLength >> 0;
-  padString = String(typeof padString !== 'undefined' ? padString : ' ');
-  if (src.length > targetLength) {
-    return String(src);
-  } else {
-    targetLength = targetLength - src.length;
-    while (targetLength > padString.length) {
-      padString += padString;
-    }
-    return String(src) + padString.slice(0, targetLength);
-  }
+  if (padString === '' || src.length > targetLength) return String(src);
+  targetLength = targetLength - src.length;
+  padString = repeatUpToLength(typeof padString !== 'undefined' ? String(padString) : ' ', targetLength);
+  return String(src) + padString.slice(0, targetLength);
 };
 
 /** @hidden */
-export const StringPadStart = (src: string, targetLength: number, padString: string) => {
-  if (src && src.padStart) return src.padStart(targetLength, padString);
+export const StringPadEnd = String.prototype.padEnd
+  ? (src: string, targetLength: number, padString: string) => src.padEnd(targetLength, padString)
+  : StringPadEndImpl;
+
+/** @hidden */
+export const StringPadStartImpl = (src: string, targetLength: number, padString: string) => {
   targetLength = targetLength >> 0;
-  padString = String(typeof padString !== 'undefined' ? padString : ' ');
-  if (src.length > targetLength) {
-    return String(src);
-  } else {
-    targetLength = targetLength - src.length;
-    while (targetLength > padString.length) {
-      padString += padString;
-    }
-    return padString.slice(0, targetLength) + String(src);
-  }
+  if (padString === '' || src.length > targetLength) return String(src);
+  targetLength = targetLength - src.length;
+  padString = repeatUpToLength(typeof padString !== 'undefined' ? String(padString) : ' ', targetLength);
+  return padString.slice(0, targetLength) + String(src);
 };
+
+/** @hidden */
+export const StringPadStart = String.prototype.padStart
+  ? (src: string, targetLength: number, padString: string) => src.padStart(targetLength, padString)
+  : StringPadStartImpl;
diff --git a/test/unit/check/polyfills.spec.ts b/test/unit/check/polyfills.spec.ts
@@ -0,0 +1,43 @@
+import * as assert from 'assert';
+import * as fc from '../../../lib/fast-check';
+
+import { ObjectEntriesImpl, StringPadEndImpl, StringPadStartImpl } from '../../../src/check/polyfills';
+
+describe('polyfills', () => {
+  describe('Object.entries', () => {
+    if (Object.entries) {
+      it('Should give the same answer as built-it entries', () =>
+        fc.assert(
+          fc.property(fc.dictionary(fc.fullUnicodeString(), fc.fullUnicodeString()), d => {
+            assert.deepStrictEqual(ObjectEntriesImpl(d), Object.entries(d));
+          })
+        ));
+    }
+  });
+  describe('String.prototype.padEnd', () => {
+    if (String.prototype.padEnd) {
+      it('Should give the same answer as built-it padEnd', () =>
+        fc.assert(
+          fc.property(
+            fc.fullUnicodeString(),
+            fc.nat(1000),
+            fc.fullUnicodeString(),
+            (src, l, pad) => StringPadEndImpl(src, l, pad) === src.padEnd(l, pad)
+          )
+        ));
+    }
+  });
+  describe('String.prototype.padStart', () => {
+    if (String.prototype.padStart) {
+      it('Should give the same answer as built-it padStart', () =>
+        fc.assert(
+          fc.property(
+            fc.fullUnicodeString(),
+            fc.nat(1000),
+            fc.fullUnicodeString(),
+            (src, l, pad) => StringPadStartImpl(src, l, pad) === src.padStart(l, pad)
+          )
+        ));
+    }
+  });
+});