Add tests for consul service discovery (#2490)

* Add tests for consul service discovery

* Add license header

* Address comments

* inline variables
* check for extra error

* Fix error formatting

discovery/consul/consul_test.go

@@ -0,0 +1,48 @@
+// Copyright 2015 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package consul
+
+import (
+	"testing"
+
+	"github.com/prometheus/prometheus/config"
+)
+
+func TestConfiguredService(t *testing.T) {
+	conf := &config.ConsulSDConfig{
+		Services: []string{"configuredServiceName"}}
+	consulDiscovery, err := NewDiscovery(conf)
+
+	if err != nil {
+		t.Errorf("Unexpected error when initialising discovery %v", err)
+	}
+	if !consulDiscovery.shouldWatch("configuredServiceName") {
+		t.Errorf("Expected service %s to be watched", "configuredServiceName")
+	}
+	if consulDiscovery.shouldWatch("nonConfiguredServiceName") {
+		t.Errorf("Expected service %s to not be watched", "nonConfiguredServiceName")
+	}
+}
+
+func TestNonConfiguredService(t *testing.T) {
+	conf := &config.ConsulSDConfig{}
+	consulDiscovery, err := NewDiscovery(conf)
+
+	if err != nil {
+		t.Errorf("Unexpected error when initialising discovery %v", err)
+	}
+	if !consulDiscovery.shouldWatch("nonConfiguredServiceName") {
+		t.Errorf("Expected service %s to be watched", "nonConfiguredServiceName")
+	}
+}