test(stats): pin the relay client's clock to the fake gateway's

go/internal/statsrelay/statsrelay.go

@@ -102,6 +102,13 @@ func New(relay string, key ohttp.KeyConfig, client *http.Client) *Client {
 	return &Client{relay: relay, key: key, http: client, now: time.Now}
 }
 
+// WithClock makes c stamp reports with the day now reads. Tests pin it to
+// the fake gateway's clock, so a fixed test date stays fresh.
+func (c *Client) WithClock(now func() time.Time) *Client {
+	c.now = now
+	return c
+}
+
 // Relay is the relay's URL, for Settings.
 func (c *Client) Relay() string { return c.relay }
 

go/internal/statsrelay/statsrelaytest/statsrelaytest.go

@@ -86,7 +86,7 @@ func New(t testing.TB, now time.Time) (*statsrelay.Client, *Gateway, *Relay) {
 		_, _ = io.Copy(w, resp.Body)
 	}))
 	t.Cleanup(rl.Close)
-	return statsrelay.New(rl.URL, g.Key, nil), g, rl
+	return statsrelay.New(rl.URL, g.Key, nil).WithClock(func() time.Time { return now }), g, rl
 }
 
 func (g *Gateway) add(msg []byte) int {