Updated the test system

test/filterNonUniqueBy.test.js

@@ -0,0 +1,36 @@
+const expect = require('expect');
+const {filterNonUniqueBy} = require('./_30s.js');
+
+test('filterNonUniqueBy is a Function', () => {
+  expect(filterNonUniqueBy).toBeInstanceOf(Function);
+});
+
+test('filterNonUniqueBy works for properties', () => {
+  expect(
+    filterNonUniqueBy(
+      [
+        { id: 0, value: 'a' },
+        { id: 1, value: 'b' },
+        { id: 2, value: 'c' },
+        { id: 1, value: 'd' },
+        { id: 0, value: 'e' }
+      ],
+      (a, b) => a.id === b.id
+    )
+  ).toEqual([{ id: 2, value: 'c' }]);
+});
+
+test('filterNonUniqueBy works for nested properties', () => {
+  expect(
+    filterNonUniqueBy(
+      [
+        { id: 0, value: 'a', n: { p: 0 } },
+        { id: 1, value: 'b', n: { p: 1 } },
+        { id: 2, value: 'c', n: { p: 2 } },
+        { id: 1, value: 'd', n: { p: 0 } },
+        { id: 0, value: 'e', n: { p: 1 } }
+      ],
+      (a, b) => a.id === b.id
+    )
+  ).toEqual([{ id: 2, value: 'c', n: { p: 2 } }]);
+});