diff --git a/package.json b/package.json
index 7d9078b..6b834a3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "nodeplotlib",
-  "version": "0.4.2",
+  "version": "0.5.0",
   "description": "NodeJS frontend-less plotting lib using plotly.js inspired by matplotlib",
   "main": "dist/lib/index.js",
   "types": "dist/lib/index.d.ts",
diff --git a/src/plot.ts b/src/plot.ts
index 2c9d9fb..1f40455 100644
--- a/src/plot.ts
+++ b/src/plot.ts
@@ -32,7 +32,7 @@ export function stack(data: Plot[], layout?: Layout): void {
  * @param layout
  * @param cb
  */
-export function plot(data?: Plot[] | null, layout?: Layout, cb?: (id: number) => void): void {
+export function plot(data?: Plot[] | null, layout?: Layout): void {
   if (data) {
     stack(data, layout);
   }
@@ -45,9 +45,5 @@ export function plot(data?: Plot[] | null, layout?: Layout, cb?: (id: number) =>
   };
   plots = [];
 
-  server.spawn(plotContainer, () => {
-    if (cb) {
-      cb(id);
-    }
-  });
+  server.spawn(plotContainer);
 }
diff --git a/src/server.ts b/src/server.ts
index 0980e6c..d4354d4 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -19,7 +19,7 @@ export class Server {
    * and opens a new browser window targetting the webservers
    * data address.
    */
-  public spawn(plotsContainer: IPlotsContainer, cb?: () => void) {
+  public spawn(plotsContainer: IPlotsContainer) {
     this.plotsContainer = plotsContainer;
 
     if (!this.instance.address()) {
@@ -27,17 +27,13 @@ export class Server {
     }
 
     this.openBrowserWindow();
-
-    if (cb) {
-      cb();
-    }
   }
 
   /**
    * Closes the webserver and clears the plots container.
    */
   public clean() {
-    if (this.instance) {
+    if (this.instance.address()) {
       this.instance.close();
     }
     this.plotsContainer = {};
diff --git a/test/clear.spec.ts b/test/clear.spec.ts
index 68b9d0b..10429d5 100644
--- a/test/clear.spec.ts
+++ b/test/clear.spec.ts
@@ -10,4 +10,11 @@ describe('clear', () => {
 
     expect(lib.plots).toEqual([]);
   });
+
+  it('should be clearable multiple times', () => {
+    lib.clear();
+    lib.clear();
+
+    expect(lib.plots).toEqual([]);
+  });
 });
diff --git a/test/server.spec.ts b/test/server.spec.ts
index 6487c5e..af7cecf 100644
--- a/test/server.spec.ts
+++ b/test/server.spec.ts
@@ -53,6 +53,67 @@ describe('Server', () => {
     });
   });
 
+  it('should serve the website and return 404 if html file not found', (done) => {
+    server.spawn({0: {
+      opened: false,
+      pending: false,
+      plots: [{data: [{ x: [1], y: [2]}]}]
+    }});
+
+    request(`http://localhost:8080/plots/0/index.html`, (err, response, body) => {
+      expect(response.statusCode).toBe(404);
+      done();
+    });
+  });
+
+  it('should serve the nodeplotlib script and return 404 if file not found', (done) => {
+    server.spawn({0: {
+      opened: false,
+      pending: false,
+      plots: [{data: [{ x: [1], y: [2]}]}]
+    }});
+
+    request(`http://localhost:8080/plots/0/nodeplotlib.min.js`, (err, response, body) => {
+      expect(response.statusCode).toBe(404);
+      done();
+    });
+  });
+
+  it('should serve the plotly.min.js script and return 404 if file not found', (done) => {
+    server.spawn({0: {
+      opened: false,
+      pending: false,
+      plots: [{data: [{ x: [1], y: [2]}]}]
+    }});
+
+    request(`http://localhost:8080/plots/0/plotly.min.js`, (err, response, body) => {
+      expect(response.statusCode).toBe(404);
+      done();
+    });
+  });
+
+  it('should not close the webserver, if one plot hasn\'t got its data', (done) => {
+    server.spawn({0: {
+      opened: false,
+      pending: false,
+      plots: [{data: [{ x: [1], y: [2]}]}]
+    },
+    1: {
+      opened: false,
+      pending: false,
+      plots: [{data: [{ x: [1], y: [3]}]}]
+    }});
+
+    request(`http://localhost:8080/data/0`, (err, response, body) => {
+      expect(JSON.parse(body)).toEqual([{data: [{ x: [1], y: [2]}]}]);
+
+      request(`http://localhost:8080/data/1`, (err1, response1, body1) => {
+        expect(JSON.parse(body1)).toEqual([{data: [{ x: [1], y: [3]}]}]);
+        done();
+      });
+    });
+  });
+
   it('should return 404 if routes not matching', (done) => {
     const data = {0: {
       opened: false,
@@ -69,14 +130,6 @@ describe('Server', () => {
     });
   });
 
-  it('should work with callback', () => {
-    const mock = jest.fn().mockImplementation(() => null);
-
-    server.spawn({}, mock);
-
-    expect(mock).toHaveBeenCalledTimes(1);
-  });
-
   afterEach(() => {
     server.clean();
     server = null;