Unfortunately frost replenishment is still not ideal on the PTR in that each frostbolt delays the next replenishment tick by 1 second. You typically only get about 60-70% of the possible ticks because of this.
Here's an example:
Replenish Since damage or
Time Event tick replenishment
32.866 CAST_START
33.867 DAMAGE
34.908 CAST_START
34.909 PERIODIC_ENERGIZE 1.042
36.065 PERIODIC_ENERGIZE 1.156 1.156
36.266 DAMAGE
36.908 CAST_START
37.465 PERIODIC_ENERGIZE 1.4 1.199
38.305 DAMAGE
38.909 CAST_START
39.346 PERIODIC_ENERGIZE 1.881 1.041
40.426 DAMAGE
41.107 CAST_START
41.465 PERIODIC_ENERGIZE 2.119 1.039
42.466 DAMAGE
43.227 CAST_START
43.425 PERIODIC_ENERGIZE 1.96 0.959
44.306 DAMAGE
45.388 CAST_START
45.389 PERIODIC_ENERGIZE 1.964 1.083
46.546 PERIODIC_ENERGIZE 1.157 1.157
46.548 DAMAGE
47.347 CAST_START
47.945 PERIODIC_ENERGIZE 1.399 1.397
48.745 DAMAGE
49.388 CAST_START
49.745 PERIODIC_ENERGIZE 1.8 1
The time between replenishment ticks ranges from 1.156 to 2.119 seconds. The longest time is probably due to erratic latency (the PTR is overseas from where I am, as far as I know, so the network latency is about 5-6 times higher than normal for me).
That's 10 ticks in roughly 16 seconds = 62.5% efficiency.
Compare that to a Retribution paladin on live (from WWS):

0:01'00.815 Tiga gains 50 Mana from Xel Replenishment. #280183
0:01'01.656 Tiga gains 49 Mana from Xel Replenishment. #280349
0:01'03.060 Tiga gains 49 Mana from Xel Replenishment. #280535
0:01'04.058 Tiga gains 50 Mana from Xel Replenishment. #280742
0:01'04.916 Tiga gains 49 Mana from Xel Replenishment. #280892
0:01'06.009 Tiga gains 49 Mana from Xel Replenishment. #281099
0:01'06.979 Tiga gains 49 Mana from Xel Replenishment. #281220
0:01'07.947 Tiga gains 49 Mana from Xel Replenishment. #281397
0:01'09.004 Tiga gains 50 Mana from Xel Replenishment. #281540
0:01'09.993 Tiga gains 50 Mana from Xel Replenishment. #281667
0:01'11.021 Tiga gains 49 Mana from Xel Replenishment. #281791
0:01'12.187 Tiga gains 50 Mana from Xel Replenishment. #281942
0:01'13.076 Tiga gains 49 Mana from Xel Replenishment. #282064
0:01'14.152 Tiga gains 50 Mana from Xel Replenishment. #282256
0:01'14.984 Tiga gains 49 Mana from Xel Replenishment. #282440
0:01'15.934 Tiga gains 50 Mana from Xel Replenishment. #282566
0:01'16.960 Tiga gains 49 Mana from Xel Replenishment. #282728
That's 17 ticks in roughly 16.1 seconds. Not 100% regular either, but one tick per second on average.