Refactor some tests (#34580)

1. use `test.MockVariableValue` as much as possible
2. avoid `time.Sleep` as much as possible

modules/auth/openid/discovery_cache_test.go

@@ -26,7 +26,8 @@ func (s *testDiscoveredInfo) OpLocalID() string {
 }
 
 func TestTimedDiscoveryCache(t *testing.T) {
-	dc := newTimedDiscoveryCache(1 * time.Second)
+	ttl := 50 * time.Millisecond
+	dc := newTimedDiscoveryCache(ttl)
 
 	// Put some initial values
 	dc.Put("foo", &testDiscoveredInfo{}) // openid.opEndpoint: "a", openid.opLocalID: "b", openid.claimedID: "c"})
@@ -41,8 +42,8 @@ func TestTimedDiscoveryCache(t *testing.T) {
 	// Attempt to get a non-existent value
 	assert.Nil(t, dc.Get("bar"))
 
-	// Sleep one second and try retrieve again
-	time.Sleep(1 * time.Second)
+	// Sleep for a while and try to retrieve again
+	time.Sleep(ttl * 3 / 2)
 
 	assert.Nil(t, dc.Get("foo"))
 }