When not passing version to resolvePackage, it should return latest.

lib/composability.js

@@ -1,4 +1,5 @@
 'use strict';
+const assert = require('assert');
 const semver = require('semver');
 const pacote = require('pacote');
 
@@ -54,19 +55,24 @@ composability.lookupLocalPackages = function (packagesToLookup = 'generator-*')
 /**
  * Resolve a package name with version.
  *
- * @param  {string} [packageName] - package to resolve.
+ * @param  {string} packageName - package to resolve.
  * @param  {string} [packageVersion] - version or range to resolve.
  * @param  {string[]} Array of key, value pairs.
  */
 composability.resolvePackage = async function (packageName, packageVersion) {
+  assert(packageName, 'Parameter packageName is required');
   if (packageVersion) {
     packageName = `${packageName}@${packageVersion}`;
   }
   const manifest = await pacote.manifest(packageName);
+  if (!manifest) {
+    return undefined;
+  }
   const from = manifest._from;
   const index = from.lastIndexOf('@');
   if (index > 1) {
-    return [from.slice(0, Math.max(0, index)), from.slice(index + 1, from.length)];
+    const resolvedVersion = from.slice(index + 1, from.length) || manifest.version;
+    return [from.slice(0, Math.max(0, index)), resolvedVersion];
   }
-  return [manifest.name, from];
+  return [manifest.name, from || manifest.version];
 };

test/composability.js

@@ -9,6 +9,15 @@ describe('composability', () => {
   });
 
   describe('resolvePackage()', () => {
+    it('should throw on missing packageName', async function () {
+      assert.rejects(async () => this.env.resolvePackage());
+    });
+
+    it('should lookup for latest package version', async function () {
+      const entry = await this.env.resolvePackage('yeoman-generator');
+      assert.ok(entry[1], 'must provide an version');
+    });
+
     it('should return package entry', async function () {
       assert.deepStrictEqual(
         await this.env.resolvePackage('yeoman-generator', '^2'),