add unit test for xarc-subapp

[zenz34]

----------------------------|---------|----------|---------|---------|------------------------------

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	83.13	73.04	70.13	83.12
browser	69.19	47.83	63.27	69.44
client-render-pipeline.ts	78.26	0	66.67	78.26	26-29,74
index.ts	57.14	45	35.71	57.38	114-158
webpack4-jsonp.ts	100	100	100	100
xarc-cdn-map.ts	96	75	100	95.83	27
xarc-subapp-v2.ts	65.22	37.93	66.67	65.67	...0,159-163,168-171,193-197
xarcv2.ts	100	100	100	100
node	90.17	86.21	78.95	90.11
index.ts	85.42	100	64.29	83.33	54-68
init-context.ts	100	100	100	100
init-v2.ts	98.46	96.88	92.31	98.46	100
load-v2.ts	100	100	100	100
render-page.ts	72	42.86	85.71	72.73	93-106
server-render-pipeline.ts	74.36	42.86	87.5	74.36	53,89-91,95-97,104-109
start-v2.ts	100	33.33	100	100	11-17
utils.ts	100	100	100	100
webpack-stats.ts	92.86	100	83.33	92.31	42
xarc-subapp-v2-node.ts	66.67	50	36.36	66.67	46,57-59
subapp	88.76	77.78	58.62	88.64
client-render-pipeline.ts	36.36	100	9.09	36.36	38-66
envhooks.ts	100	100	100	100
index.ts	97.5	88.89	83.33	97.5	52
subapp-ready.ts	91.3	56.25	83.33	90.91	80-81
types.ts	100	100	100	100
----------------------------	---------	----------	---------	---------	------------------------------

=============================== Coverage summary ===============================
Statements : 83.13% ( 473/569 )
Branches : 73.04% ( 168/230 )
Functions : 70.13% ( 108/154 )
Lines : 83.12% ( 458/551 )

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