diff --git a/packages/build/src/npm-packages.spec.ts b/packages/build/src/npm-packages.spec.ts
new file mode 100644
index 000000000..7b5f42646
--- /dev/null
+++ b/packages/build/src/npm-packages.spec.ts
@@ -0,0 +1,13 @@
+import { expect } from 'chai';
+import { listNpmPackages } from './npm-packages';
+
+describe('listNpmPackages', () => {
+  it('lists packages', () => {
+    const packages = listNpmPackages();
+    expect(packages.length).to.be.greaterThan(1);
+    for (const { name, version } of packages) {
+      expect(name).to.be.a('string');
+      expect(version).to.be.a('string');
+    }
+  });
+});
diff --git a/packages/build/src/npm-packages.ts b/packages/build/src/npm-packages.ts
index 378da591d..fe1d5ca62 100644
--- a/packages/build/src/npm-packages.ts
+++ b/packages/build/src/npm-packages.ts
@@ -55,16 +55,17 @@ export function publishNpmPackages(): void {
   });
 }
 
-function listNpmPackages(): {version: string}[] {
+export function listNpmPackages(): {name: string; version: string}[] {
   const lernaListOutput = spawn.sync(
     LERNA_BIN, [
       'list',
       '--json',
     ],
     {
-      cwd: PROJECT_ROOT
+      cwd: PROJECT_ROOT,
+      encoding: 'utf8'
     }
-  ).toString();
+  );
 
-  return JSON.parse(lernaListOutput);
+  return JSON.parse(lernaListOutput.stdout);
 }