Add timeout error for influx

This adds a type to be returned when requests to InfluxDB were cancelled
or timed out.

influx/errors.go

@@ -0,0 +1,13 @@
+package influx
+
+const (
+	ErrTimedOut string = "Timeout during request to InfluxDB"
+)
+
+// TimeoutError is returned when requests to InfluxDB are cancelled or time
+// out.
+type TimeoutError struct{}
+
+func (te TimeoutError) Error() string {
+	return ErrTimedOut
+}

influx/influx.go

@@ -43,6 +43,6 @@ func (c *Client) Query(ctx context.Context, query mrfusion.Query) (mrfusion.Resp
 	case resp := <-resps:
 		return resp, resp.err
 	case <-ctx.Done():
-		return nil, nil
+		return nil, TimeoutError{}
 	}
 }

influx/influx_test.go

@@ -66,8 +66,10 @@ func Test_Influx_CancelsInFlightRequests(t *testing.T) {
 	series, _ := influx.NewClient(ts.URL)
 	ctx, cancel := context.WithCancel(context.Background())
 
+	errs := make(chan (error))
 	go func() {
-		_, _ = series.Query(ctx, "show databases")
+		_, err := series.Query(ctx, "show databases")
+		errs <- err
 	}()
 
 	cancel()
@@ -75,4 +77,9 @@ func Test_Influx_CancelsInFlightRequests(t *testing.T) {
 	if started != true && finished != false {
 		t.Errorf("Expected cancellation during request processing. Started: %t. Finished: %t", started, finished)
 	}
+
+	err := <-errs
+	if _, ok := err.(influx.TimeoutError); !ok {
+		t.Error("Expected TimeoutError but wasn't. err was", err)
+	}
 }