Hide environment external URL button if not defined

app/views/projects/environments/terminal.html.haml

@@ -16,6 +16,7 @@
 
       .col-sm-6
         .nav-controls
+          - if @environment.external_url.present?
             = link_to @environment.external_url, class: 'btn btn-default', target: '_blank', rel: 'noopener noreferrer nofollow' do
               = icon('external-link')
           = render 'projects/deployments/actions', deployment: @environment.last_deployment

spec/views/projects/environments/terminal.html.haml_spec.rb

+require 'spec_helper'
+
+describe 'projects/environments/terminal' do
+  let!(:environment) { create(:environment, :with_review_app) }
+
+  before do
+    assign(:environment, environment)
+    assign(:project, environment.project)
+
+    allow(view).to receive(:can?).and_return(true)
+  end
+
+  context 'when environment has external URL' do
+    it 'shows external URL button' do
+      environment.update_attribute(:external_url, 'https://gitlab.com')
+
+      render
+
+      expect(rendered).to have_link(nil, href: 'https://gitlab.com')
+    end
+  end
+
+  context 'when environment does not have external URL' do
+    it 'shows external URL button' do
+      environment.update_attribute(:external_url, nil)
+
+      render
+
+      expect(rendered).not_to have_link(nil, href: 'https://gitlab.com')
+    end
+  end
+end