diff --git a/lib/server.js b/lib/server.js
index b56adbe..72fb513 100644
--- a/lib/server.js
+++ b/lib/server.js
@@ -62,9 +62,9 @@ export default class AppManagerServer {
     return params;
   };
 
-  _parseQuery = (query: string | QueryType) => (typeof query === 'object' ? query : qs.parse(query));
+  _parseQuery = (query: string | QueryType = {}) => (typeof query === 'object' ? query : qs.parse(query));
 
-  init = async (path: string, query: string | QueryType, ...getMarkupArgs: Array<mixed>): Promise<any> => {
+  init = async (path: string, query?: string | QueryType, ...getMarkupArgs: Array<mixed>): Promise<any> => {
     const currentAppName = this._getAppNameFromPath(path);
 
     if (!currentAppName) {
@@ -87,7 +87,7 @@ export default class AppManagerServer {
       const fragmentName = appFragments[slotName];
       const fragment = this._fragments[fragmentName];
 
-      const markup = typeof fragment.getMarkup === 'function' ? await fragment.getMarkup(state, ...getMarkupArgs) : '';
+      const markup = fragment && typeof fragment.getMarkup === 'function' ? await fragment.getMarkup(state, ...getMarkupArgs) : '';
 
       return { slotName, markup };
     });
diff --git a/package-lock.json b/package-lock.json
index 3421552..728cacb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "app-manager",
-  "version": "0.19.2",
+  "version": "0.19.3",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
@@ -2734,6 +2734,15 @@
         "type-detect": "4.0.3"
       }
     },
+    "chai-as-promised": {
+      "version": "7.1.1",
+      "resolved": "https://registry.npmjs.org/chai-as-promised/-/chai-as-promised-7.1.1.tgz",
+      "integrity": "sha512-azL6xMoi+uxu6z4rhWQ1jbdUhOMhis2PvscD/xjLqNMkv3BPPp2JyyuTHOrf9BOosGpNQ11v6BKv/g57RXbiaA==",
+      "dev": true,
+      "requires": {
+        "check-error": "1.0.2"
+      }
+    },
     "chalk": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/chalk/-/chalk-2.3.0.tgz",
@@ -8001,7 +8010,7 @@
         "lolex": "2.3.2",
         "nise": "1.2.2",
         "supports-color": "5.1.0",
-        "type-detect": "4.0.7"
+        "type-detect": "4.0.8"
       },
       "dependencies": {
         "lodash.get": {
@@ -8020,9 +8029,9 @@
           }
         },
         "type-detect": {
-          "version": "4.0.7",
-          "resolved": "https://registry.npmjs.org/type-detect/-/type-detect-4.0.7.tgz",
-          "integrity": "sha512-4Rh17pAMVdMWzktddFhISRnUnFIStObtUMNGzDwlA6w/77bmGv3aBbRdCmQR6IjzfkTo9otnW+2K/cDRhKSxDA==",
+          "version": "4.0.8",
+          "resolved": "https://registry.npmjs.org/type-detect/-/type-detect-4.0.8.tgz",
+          "integrity": "sha512-0fr/mIH1dlO+x7TlcMy+bIDqKPsw/70tVyeHW787goQjhmqaZe10uwLujubK9q9Lg6Fiho1KUKDYz0Z7k7g5/g==",
           "dev": true
         }
       }
diff --git a/package.json b/package.json
index e0c925c..41894f9 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "app-manager",
-  "version": "0.19.3",
+  "version": "0.19.4",
   "description": "Script for managing the lifecycles of multiple apps on a single page",
   "main": "es5/index.js",
   "scripts": {
@@ -35,10 +35,10 @@
   "homepage": "https://github.com/tomruttle/app-manager#readme",
   "nyc": {
     "check-coverage": true,
-    "lines": 70,
-    "statements": 70,
+    "lines": 80,
+    "statements": 80,
     "functions": 100,
-    "branches": 64,
+    "branches": 70,
     "include": [
       "lib/**"
     ],
@@ -59,6 +59,7 @@
     "babel-preset-flow": "^6.23.0",
     "babel-register": "^6.26.0",
     "chai": "^4.1.2",
+    "chai-as-promised": "^7.1.1",
     "env-test": "^1.0.0",
     "eslint": "^4.16.0",
     "eslint-config-airbnb-base": "^12.1.0",
diff --git a/test/server.test.js b/test/server.test.js
new file mode 100644
index 0000000..9e81dec
--- /dev/null
+++ b/test/server.test.js
@@ -0,0 +1,94 @@
+// @flow
+
+import chai, { expect } from 'chai';
+import chaiAsPromised from 'chai-as-promised';
+import sinon from 'sinon';
+
+import AppManagerServer from '../lib/server';
+
+chai.use(chaiAsPromised);
+
+describe('Server', () => {
+  function getConfig() {
+    return {
+      apps: {
+        app_a: {
+          name: 'app_a',
+          fragments: ['fragment_a'],
+          appPath: '/app-a',
+        },
+        app_b: {
+          name: 'app_b',
+          fragments: ['fragment_b'],
+          appPath: '/app-b/:param1?',
+        },
+      },
+      fragments: {
+        fragment_a: {
+          name: 'fragment_a',
+          managed: true,
+          slots: ['app'],
+          loadScript: () => { throw new Error('Should not be called.'); },
+          getMarkup: sinon.stub().returns(Promise.resolve('fragment_a')),
+        },
+        fragment_b: {
+          name: 'fragment_b',
+          managed: true,
+          slots: ['app'],
+          loadScript: () => { throw new Error('Should not be called.'); },
+          getMarkup: sinon.stub().returns(Promise.resolve('fragment_b')),
+        },
+      },
+      slots: {
+        app: { name: 'app', querySelector: null },
+        other: { name: 'other', querySelector: null },
+      },
+    };
+  }
+
+  describe('init', () => {
+    it('rejects if path does not match any apps', () => {
+      const appManagerServer = new AppManagerServer(getConfig());
+      expect(appManagerServer.init('/app-c')).be.rejectedWith('server.invalid_appPath');
+    });
+
+    it('returns the async return value of getMarkup for the correct app in the correct slot', async () => {
+      const config = getConfig();
+      const appManagerServer = new AppManagerServer(config);
+      const appMarkup = await appManagerServer.init('/app-a');
+
+      expect(appMarkup).to.deep.equals({ app: 'fragment_a', other: '' });
+
+      const getMarkupStubB = config.fragments.fragment_b.getMarkup;
+      expect(getMarkupStubB.called).to.be.false;
+
+      const getMarkupStubA = config.fragments.fragment_a.getMarkup;
+      expect(getMarkupStubA.calledOnce).to.be.true;
+
+      const args = getMarkupStubA.args[0];
+      expect(args).to.be.an('array').with.length(1);
+      expect(args[0].app.name).to.equals('app_a');
+    });
+
+    it('can handle params, query params, and additional arguments', async () => {
+      const config = getConfig();
+      const appManagerServer = new AppManagerServer(config);
+      const appMarkup = await appManagerServer.init('/app-b/test', 'query=success', 'additional data');
+
+      expect(appMarkup).to.deep.equals({ app: 'fragment_b', other: '' });
+
+      const getMarkupStubA = config.fragments.fragment_a.getMarkup;
+      expect(getMarkupStubA.called).to.be.false;
+
+      const getMarkupStubB = config.fragments.fragment_b.getMarkup;
+      expect(getMarkupStubB.calledOnce).to.be.true;
+
+      const args = getMarkupStubB.args[0];
+      expect(args).to.be.an('array').with.length(2);
+      expect(args[0].app.name).to.equals('app_b');
+      expect(args[0].params).to.deep.equals({ param1: 'test' });
+      expect(args[0].query).to.deep.equals({ query: 'success' });
+      expect(args[1]).to.equals('additional data');
+    });
+  });
+});