Add constructFrom tests (#3559)

Co-authored-by: Sasha Koss <koss@nocorp.me>

src/constructFrom/test.ts

@@ -0,0 +1,48 @@
+import assert from "assert";
+import { describe, it } from "vitest";
+import { constructFrom } from ".";
+
+describe("constructFrom", () => {
+  it("should create a new Date instance using the constructor from the reference date", () => {
+    const referenceDate = new Date("2023-10-25T12:00:00");
+    const value = new Date("2023-10-26T12:00:00");
+
+    const result = constructFrom(referenceDate, value);
+
+    assert.ok(result instanceof Date);
+    assert.deepStrictEqual(result, value);
+    assert.strictEqual(result.constructor, referenceDate.constructor);
+  });
+
+  it("should create a new Date instance using a number as the reference date", () => {
+    const referenceDate = 1635158400000; // October 25, 2023
+    const value = new Date("2023-10-26T12:00:00");
+
+    const result = constructFrom(referenceDate, value);
+
+    assert.ok(result instanceof Date);
+    assert.deepStrictEqual(result, value);
+  });
+
+  it("should create a new custom Date instance using the constructor from the reference date", () => {
+    class CustomDate extends Date {}
+    const referenceDate = new CustomDate("2023-10-25T12:00:00");
+    const value = new CustomDate("2023-10-26T12:00:00");
+
+    const result = constructFrom(referenceDate, value);
+
+    assert.ok(result instanceof CustomDate);
+    assert.deepStrictEqual(result, value);
+    assert.strictEqual(result.constructor, referenceDate.constructor);
+  });
+
+  it("should create a new Date instance using numbers as both referenceDate and value", () => {
+    const referenceDate = 1635158400000; // October 25, 2023
+    const value = 1635244800000; // October 26, 2023
+
+    const result = constructFrom(referenceDate, value);
+
+    assert.ok(result instanceof Date);
+    assert.deepStrictEqual(result.getTime(), value);
+  });
+});