Add test for overwrite

__tests__/auth.test.ts

@@ -42,7 +42,26 @@ describe('auth tests', () => {
     );
   }, 100000);
 
-  it('does not create settings.xml without username and / or password', async () => {
+  it('overwrites existing settings.xml files', async () => {
+    const id = 'packages';
+    const username = 'bluebottle';
+    const password = 'SingleOrigin';
+
+    fs.mkdirSync(m2Dir, {recursive: true});
+    fs.writeFileSync(settingsFile, "FAKE FILE");
+    expect(fs.existsSync(m2Dir)).toBe(true);
+    expect(fs.existsSync(settingsFile)).toBe(true);
+
+    await auth.configAuthentication(id, username, password);
+
+    expect(fs.existsSync(m2Dir)).toBe(true);
+    expect(fs.existsSync(settingsFile)).toBe(true);
+    expect(fs.readFileSync(settingsFile, 'utf-8')).toEqual(
+      auth.generate(id, username, password)
+    );
+  }, 100000);
+
+  it('does not create settings.xml without required parameters', async () => {
     await auth.configAuthentication('FOO', '', '');
 
     expect(fs.existsSync(m2Dir)).toBe(false);