Improve naming of a util function & add unit test

isOlderThan -> isValidDateAndOlderThan

See: https://github.com/balena-os/balena-supervisor/pull/2170#discussion_r1226809686
Signed-off-by: Christina Ying Wang <christina@balena.io>

src/compose/app.ts

@@ -12,7 +12,7 @@ import {
 	generateStep,
 	CompositionStepAction,
 } from './composition-steps';
-import { isOlderThan } from './utils';
+import { isValidDateAndOlderThan } from './utils';
 import * as targetStateCache from '../device-state/target-state-cache';
 import { getNetworkGateway } from '../lib/docker-utils';
 import * as constants from '../lib/constants';
@@ -671,7 +671,7 @@ export class App {
 		} else if (target.config.running !== current.config.running) {
 			if (
 				this.requirementsMetForSpecialStart(current, target) &&
-				!isOlderThan(current.createdAt, SECONDS_TO_WAIT_FOR_START)
+				!isValidDateAndOlderThan(current.createdAt, SECONDS_TO_WAIT_FOR_START)
 			) {
 				return generateStep('noop', {});
 			}

src/compose/utils.ts

@@ -694,8 +694,20 @@ export function dockerMountToServiceMount(
 	return mount as LongDefinition;
 }
 
-export function isOlderThan(currentTime: Date | null, seconds: number) {
-	if (currentTime == null) {
+function isDate(d: unknown): d is Date {
+	return d instanceof Date;
+}
+
+/**
+ * @param currentTime Date instance
+ * @param seconds time in seconds to check against currentTime
+ * @returns
+ */
+export function isValidDateAndOlderThan(
+	currentTime: unknown,
+	seconds: number,
+): boolean {
+	if (!isDate(currentTime)) {
 		return false;
 	}
 	return new Date().getTime() - currentTime.getTime() > seconds * 1000;

test/unit/compose/utils.spec.ts

@@ -1,8 +1,8 @@
 import { expect } from 'chai';
 import * as ComposeUtils from '~/src/compose/utils';
 
-describe('compose/utils', () =>
-	it('Should correctly camel case the configuration', function () {
+describe('compose/utils', () => {
+	it('should correctly camel case the configuration', () => {
 		const config = {
 			networks: ['test', 'test2'],
 		};
@@ -10,4 +10,34 @@ describe('compose/utils', () =>
 		expect(ComposeUtils.camelCaseConfig(config)).to.deep.equal({
 			networks: ['test', 'test2'],
 		});
-	}));
+	});
+
+	it('should return whether a date is valid and older than an interval of seconds', () => {
+		const now = new Date(Date.now());
+		expect(ComposeUtils.isValidDateAndOlderThan(now, 60)).to.equal(false);
+		const time59SecondsAgo = new Date(Date.now() - 59 * 1000);
+		expect(ComposeUtils.isValidDateAndOlderThan(time59SecondsAgo, 60)).to.equal(
+			false,
+		);
+		const time61SecondsAgo = new Date(Date.now() - 61 * 1000);
+		expect(ComposeUtils.isValidDateAndOlderThan(time61SecondsAgo, 60)).to.equal(
+			true,
+		);
+
+		const notDates = [
+			null,
+			undefined,
+			'',
+			'test',
+			123,
+			0,
+			-1,
+			Infinity,
+			NaN,
+			{},
+		];
+		notDates.forEach((n) => {
+			expect(ComposeUtils.isValidDateAndOlderThan(n, 0)).to.equal(false);
+		});
+	});
+});