Add schema validation spec

Validate the schema of the dashboard that is loaded by
Gitlab::MetricsDashboard::Service.

spec/fixtures/lib/gitlab/metrics_dashboard/schemas/dashboard.json

+{
+  "type": "object",
+  "required": [
+    "dashboard",
+    "order",
+    "panel_groups"
+  ],
+  "properties": {
+    "dashboard": { "type": "string" },
+    "order": { "type": "number" },
+    "panel_groups": {
+      "type": "array",
+      "items": { "$ref": "spec/fixtures/lib/gitlab/metrics_dashboard/schemas/panel_groups.json" }
+    }
+  },
+  "additionalProperties": false
+}

spec/fixtures/lib/gitlab/metrics_dashboard/schemas/metrics.json

+{
+  "type": "object",
+  "required": [
+    "unit",
+    "label"
+  ],
+  "properties": {
+    "id": { "type": "string" },
+    "query_range": { "type": "string" },
+    "query": { "type": "string" },
+    "unit": { "type": "string" },
+    "label": { "type": "string" },
+    "track": { "type": "string" }
+  },
+  "additionalProperties": false
+}

spec/fixtures/lib/gitlab/metrics_dashboard/schemas/panel_groups.json

+{
+  "type": "object",
+  "required": [
+    "group",
+    "priority",
+    "panels"
+  ],
+  "properties": {
+    "group": { "type": "string" },
+    "priority": { "type": "number" },
+    "panels": {
+      "type": "array",
+      "items": { "$ref": "panels.json" }
+    }
+  },
+  "additionalProperties": false
+}

spec/fixtures/lib/gitlab/metrics_dashboard/schemas/panels.json

+{
+  "type": "object",
+  "required": [
+    "title",
+    "y_label",
+    "weight",
+    "metrics"
+  ],
+  "properties": {
+    "title": { "type": "string" },
+    "type": { "type": "string" },
+    "y_label": { "type": "string" },
+    "weight": { "type": "number" },
+    "metrics": {
+      "type": "array",
+      "items": { "$ref": "metrics.json" }
+    }
+  },
+  "additionalProperties": false
+}

spec/lib/gitlab/metrics_dashboard/service_spec.rb

@@ -6,14 +6,15 @@ describe Gitlab::MetricsDashboard::Service, :use_clean_rails_memory_store_cachin
   let(:project) { build(:project) }
 
   describe 'get_dashboard' do
+    let(:dashboard_schema) { JSON.parse(fixture_file('lib/gitlab/metrics_dashboard/schemas/dashboard.json')) }
+
     it 'returns a json representation of the environment dashboard' do
       result = described_class.new(project).get_dashboard
 
       expect(result.keys).to contain_exactly(:dashboard, :status)
       expect(result[:status]).to eq(:success)
 
-      expect(result[:dashboard]).to include('dashboard', 'order', 'panel_groups')
-      expect(result[:dashboard]['panel_groups']).to all( include('group', 'priority', 'panels') )
+      expect(JSON::Validator.fully_validate(dashboard_schema, result[:dashboard])).to be_empty
     end
 
     it 'caches the dashboard for subsequent calls' do