diff --git a/spec/main.spec.ts b/spec/main.spec.ts
index 9ff1cce..2a2d4bb 100644
--- a/spec/main.spec.ts
+++ b/spec/main.spec.ts
@@ -134,8 +134,9 @@ describe('main', () => {
   });
 
   describe('#mockConfig', () => {
-    after(() => {
+    afterEach(() => {
       delete process.env.CLOUD_RUNTIME_CONFIG;
+      delete functions.config.singleton;
     });
 
     it('should mock functions.config()', () => {
@@ -143,5 +144,11 @@ describe('main', () => {
       mockConfig(config);
       expect(functions.config()).to.deep.equal(config);
     });
+
+    it('should allow multiple mock configurations', () => {
+      const config = { baz: { qux: 'quxx ' } };
+      mockConfig(config);
+      expect(functions.config()).to.deep.equal(config);
+    });
   });
 });