adding additional unit tests for getDataCenter() in consul (#6192)

* adding additional unit tests for getDataCenter() in consul

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

* Consult Tests : update comments to start with uppercase and end with point

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

* Consult Test : using table-driven tests

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

* Consul Test : cleaner syntax

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

* Consul Test : even cleaner syntax

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

* Consul Test : update comments

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

* Fixing naming convention by removing underscore in function name

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

* Removing duplicated test case for getDatacenter()

Signed-off-by: Jean-Baptiste Le Duigou <jb.leduigou@gmail.com>

discovery/consul/consul_test.go

@@ -297,3 +297,47 @@ func TestAllOptions(t *testing.T) {
 	checkOneTarget(t, <-ch)
 	cancel()
 }
+
+func TestGetDatacenterShouldReturnError(t *testing.T) {
+	for _, tc := range []struct {
+		handler    func(http.ResponseWriter, *http.Request)
+		errMessage string
+	}{
+		{
+			// Define a handler that will return status 500.
+			handler: func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(500)
+			},
+			errMessage: "Unexpected response code: 500 ()",
+		},
+		{
+			// Define a handler that will return incorrect response.
+			handler: func(w http.ResponseWriter, r *http.Request) {
+				w.Write([]byte(`{"Config": {"Not-Datacenter": "test-dc"}}`))
+			},
+			errMessage: "invalid value '<nil>' for Config.Datacenter",
+		},
+	} {
+		stub := httptest.NewServer(http.HandlerFunc(tc.handler))
+		stuburl, err := url.Parse(stub.URL)
+		testutil.Ok(t, err)
+
+		config := &SDConfig{
+			Server:          stuburl.Host,
+			Token:           "fake-token",
+			RefreshInterval: model.Duration(1 * time.Second),
+		}
+		defer stub.Close()
+		d := newDiscovery(t, config)
+
+		// Should be empty if not initialized.
+		testutil.Equals(t, "", d.clientDatacenter)
+
+		err = d.getDatacenter()
+
+		// An error should be returned.
+		testutil.Equals(t, tc.errMessage, err.Error())
+		// Should still be empty.
+		testutil.Equals(t, "", d.clientDatacenter)
+	}
+}