Adds API tests

spec/fixtures/api/schemas/statistics.json

+{
+  "type": "object",
+  "required" : [
+    "forks",
+    "issues",
+    "merge_requests",
+    "notes",
+    "snippets",
+    "ssh_keys",
+    "milestones",
+    "users",
+    "projects",
+    "groups",
+    "active_users"
+  ],
+  "properties" : {
+    "forks": { "type": "string" },
+    "issues'": { "type": "string" },
+    "merge_requests'": { "type": "string" },
+    "notes'": { "type": "string" },
+    "snippets'": { "type": "string" },
+    "ssh_keys'": { "type": "string" },
+    "milestones'": { "type": "string" },
+    "users'": { "type": "string" },
+    "projects'": { "type": "string" },
+    "groups'": { "type": "string" },
+    "active_users'": { "type": "string" }
+  }
+}

spec/requests/api/statistics_spec.rb

+require 'spec_helper'
+
+describe API::Statistics, 'Statistics' do
+  let(:path) { "/application/statistics" }
+
+  describe "GET /application/statistics" do
+    context 'when no user' do
+      it "returns authentication error" do
+        get api(path, nil)
+
+        expect(response).to have_gitlab_http_status(401)
+      end
+    end
+
+    context "when not an admin" do
+      let(:user) { create(:user) }
+
+      it "returns forbidden error" do
+        get api(path, user)
+
+        expect(response).to have_gitlab_http_status(403)
+      end
+    end
+
+    context 'when authenticated as admin' do
+      let(:admin) { create(:admin) }
+
+      it 'matches the response schema' do
+        get api(path, admin)
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(response).to match_response_schema('statistics')
+      end
+
+      it 'gives the right statistics' do
+        projects = create_list(:project, 4, namespace: create(:namespace, owner: admin))
+        issues = create_list(:issue, 2, project: projects.first, updated_by: admin)
+
+        create_list(:group, 2)
+        create_list(:snippet, 2, :public, author: admin)
+        create_list(:note, 2, author: admin, project: projects.first, noteable: issues.first)
+        create_list(:milestone, 3, project: projects.first)
+        create(:key, user: admin)
+        create(:merge_request, source_project: projects.first)
+
+        get api(path, admin)
+
+        expect(json_response['issues']).to eq('2')
+        expect(json_response['merge_requests']).to eq('1')
+        expect(json_response['notes']).to eq('2')
+        expect(json_response['snippets']).to eq('2')
+        expect(json_response['forks']).to eq('0')
+        expect(json_response['ssh_keys']).to eq('1')
+        expect(json_response['milestones']).to eq('3')
+        expect(json_response['users']).to eq('1')
+        expect(json_response['projects']).to eq('4')
+        expect(json_response['groups']).to eq('2')
+        expect(json_response['active_users']).to eq('1')
+      end
+    end
+  end
+end