Refactor device-state healthchecks to log reason for failure

Closes: #1292
Change-type: minor
Signed-off-by: Miguel Casqueira <miguel@balena.io>

src/device-state.ts

@@ -1,5 +1,6 @@
 import * as Bluebird from 'bluebird';
 import * as bodyParser from 'body-parser';
+import { stripIndent } from 'common-tags';
 import { EventEmitter } from 'events';
 import * as express from 'express';
 import * as _ from 'lodash';
@@ -285,19 +286,36 @@ export class DeviceState extends (EventEmitter as new () => DeviceStateEventEmit
 
 	public async healthcheck() {
 		const unmanaged = await this.config.get('unmanaged');
+
+		// Don't have to perform checks for unmanaged
+		if (unmanaged) {
+			return true;
+		}
+
 		const cycleTime = process.hrtime(this.lastApplyStart);
 		const cycleTimeMs = cycleTime[0] * 1000 + cycleTime[1] / 1e6;
-
 		const cycleTimeWithinInterval =
 			cycleTimeMs - this.applications.timeSpentFetching < 2 * this.maxPollTime;
 
+		// Check if target is healthy
 		const applyTargetHealthy =
-			unmanaged ||
 			!this.applyInProgress ||
 			this.applications.fetchesInProgress > 0 ||
 			cycleTimeWithinInterval;
 
-		return applyTargetHealthy;
+		if (!applyTargetHealthy) {
+			log.info(
+				stripIndent`
+				Healthcheck failure - Atleast ONE of the following conditions must be true:
+					- No applyInProgress      ? ${!(this.applyInProgress === true)}
+					- fetchesInProgress       ? ${this.applications.fetchesInProgress > 0}
+					- cycleTimeWithinInterval ? ${cycleTimeWithinInterval}`,
+			);
+			return false;
+		}
+
+		// All tests pass!
+		return true;
 	}
 
 	public async init() {

test/05-device-state.spec.ts

@@ -1,23 +1,22 @@
 import * as Bluebird from 'bluebird';
+import { stripIndent } from 'common-tags';
 import * as _ from 'lodash';
-import { stub } from 'sinon';
+import { SinonSpy, SinonStub, spy, stub } from 'sinon';
 
 import chai = require('./lib/chai-config');
 import prepare = require('./lib/prepare');
-// tslint:disable-next-line
-chai.use(require('chai-events'));
-
-const { expect } = chai;
-
+import Log from '../src/lib/supervisor-console';
 import Config from '../src/config';
 import { RPiConfigBackend } from '../src/config/backend';
 import DeviceState from '../src/device-state';
-
 import { loadTargetFromFile } from '../src/device-state/preload';
-
 import Service from '../src/compose/service';
 import { intialiseContractRequirements } from '../src/lib/contracts';
 
+// tslint:disable-next-line
+chai.use(require('chai-events'));
+const { expect } = chai;
+
 const mockedInitialConfig = {
 	RESIN_SUPERVISOR_CONNECTIVITY_CHECK: 'true',
 	RESIN_SUPERVISOR_DELTA: 'false',
@@ -384,4 +383,63 @@ describe('deviceState', () => {
 	it('applies the target state for device config');
 
 	it('applies the target state for applications');
+
+	describe('healthchecks', () => {
+		let configStub: SinonStub;
+		let infoLobSpy: SinonSpy;
+
+		beforeEach(() => {
+			// This configStub will be modified in each test case so we can
+			// create the exact conditions we want to for testing healthchecks
+			configStub = stub(Config.prototype, 'get');
+			infoLobSpy = spy(Log, 'info');
+		});
+
+		afterEach(() => {
+			configStub.restore();
+			infoLobSpy.restore();
+		});
+
+		it('passes with correct conditions', async () => {
+			// Setup passing condition
+			const previousValue = deviceState.applyInProgress;
+			deviceState.applyInProgress = false;
+			expect(await deviceState.healthcheck()).to.equal(true);
+			// Restore value
+			deviceState.applyInProgress = previousValue;
+		});
+
+		it('passes if unmanaged is true and exit early', async () => {
+			// Setup failing conditions
+			const previousValue = deviceState.applyInProgress;
+			deviceState.applyInProgress = true;
+			// Verify this causes healthcheck to fail
+			expect(await deviceState.healthcheck()).to.equal(false);
+			// Do it again but set unmanaged to true
+			configStub.resolves({
+				unmanaged: true,
+			});
+			expect(await deviceState.healthcheck()).to.equal(true);
+			// Restore value
+			deviceState.applyInProgress = previousValue;
+		});
+
+		it('fails when applyTargetHealthy is false', async () => {
+			// Copy previous values to restore later
+			const previousValue = deviceState.applyInProgress;
+			// Setup failing conditions
+			deviceState.applyInProgress = true;
+			expect(await deviceState.healthcheck()).to.equal(false);
+			expect(Log.info).to.be.calledOnce;
+			expect((Log.info as SinonSpy).lastCall?.lastArg).to.equal(
+				stripIndent`
+				Healthcheck failure - Atleast ONE of the following conditions must be true:
+					- No applyInProgress      ? false
+					- fetchesInProgress       ? false
+					- cycleTimeWithinInterval ? false`,
+			);
+			// Restore value
+			deviceState.applyInProgress = previousValue;
+		});
+	});
 });

test/11-api-binder.spec.ts

@@ -286,8 +286,8 @@ describe('ApiBinder', () => {
 		let configStub: SinonStub;
 		let infoLobSpy: SinonSpy;
 
-		before(() => {
-			initModels(components, '/config-apibinder.json');
+		before(async () => {
+			await initModels(components, '/config-apibinder.json');
 		});
 
 		beforeEach(() => {