Add more test coverage for compose/images

Closes: #1492
Change-type: patch
Signed-off-by: Miguel Casqueira <miguel@balena.io>

test/lib/mocked-dbus.ts

@@ -0,0 +1,28 @@
+import * as dbus from 'dbus';
+import { DBusError, DBusInterface } from 'dbus';
+import { stub } from 'sinon';
+
+stub(dbus, 'getBus').returns({
+	getInterface: (
+		_serviceName: string,
+		_objectPath: string,
+		_interfaceName: string,
+		interfaceCb: (err: null | DBusError, iface: DBusInterface) => void,
+	) => {
+		interfaceCb(null, {
+			Get: (
+				_unitName: string,
+				_property: string,
+				getCb: (err: null | Error, value: unknown) => void,
+			) => {
+				getCb(null, 'this is the value');
+			},
+			GetUnit: (
+				_unitName: string,
+				getUnitCb: (err: null | Error, unitPath: string) => void,
+			) => {
+				getUnitCb(null, 'this is the unit path');
+			},
+		} as any);
+	},
+} as any);