Add spec for writeManifest method of package module

 🐿 v2.10.0

src/package.js

@@ -7,15 +7,8 @@ const writeFile = util.promisify(fs.writeFile);
 
 class Package {
 	constructor (manifest, location) {
-		// define read-only properties
-		Object.defineProperties(this, {
-			manifest: {
-				value: Object.freeze(manifest)
-			},
-			location: {
-				value: path.normalize(location)
-			}
-		});
+		this.manifest = Object.freeze(manifest);
+		this.location = path.normalize(location);
 	}
 
 	get name () {
@@ -41,7 +34,7 @@ class Package {
 	async writeManifest (manifest) {
 		const json = JSON.stringify(manifest, null, 2);
 		await writeFile(this.manifestLocation, json);
-		this.manifest = manifest;
+		this.manifest = Object.freeze(manifest);
 	}
 }
 

test/src/package.spec.js

@@ -1,3 +1,6 @@
+jest.mock('fs');
+
+const fs = require('fs');
 const Subject = require('../../src/package');
 
 const fixture = Object.freeze({
@@ -49,4 +52,29 @@ describe('src/package', () => {
 			expect(instance.nodeModulesLocation).toEqual('/root/path/to/package/node_modules');
 		});
 	});
+
+	describe('#writeManifest', () => {
+		beforeEach(() => {
+			// The final arg is a callback that needs calling!
+			fs.writeFile.mockImplementation((...args) => args[args.length - 1]());
+		});
+
+		it('writes the new manifest', async () => {
+			const instance = factory(fixture);
+			await instance.writeManifest({ ...fixture, version: '1.0.0' });
+
+			expect(fs.writeFile).toHaveBeenCalledWith(
+				'/root/path/to/package/package.json',
+				JSON.stringify({ name : 'my-package', version: '1.0.0' }, null, 2),
+				expect.any(Function)
+			);
+		});
+
+		it('updates the manifest property', async () => {
+			const instance = factory(fixture);
+			await instance.writeManifest({ ...fixture, version: '1.0.0' });
+
+			expect(instance.manifest.version).toEqual('1.0.0');
+		});
+	});
 });