test: more robust integration test

[yqrashawn]

This change is 

[codecov]

Codecov Report

Merging #678 (a6ba938) into dev (9fe0f3c) will increase coverage by 13.48%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##              dev     #678       +/-   ##
===========================================
+ Coverage   29.86%   43.34%   +13.48%     
===========================================
  Files         517      517               
  Lines       27861    27861               
  Branches     1196     1871      +675     
===========================================
+ Hits         8321    12077     +3756     
+ Misses      19372    15611     -3761     
- Partials      168      173        +5     

Flag	Coverage Δ
integrationtests	32.40% <ø> (?)
unittests	29.86% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/rpc-engine/src/error.js	79.66% <0.00%> (+3.38%)	⬆️
...ackages/rpcs/cfx_estimateGasAndCollateral/index.js	100.00% <0.00%> (+3.63%)	⬆️
packages/rpcs/wallet_getAccountGroup/index.js	94.28% <0.00%> (+4.28%)	⬆️
packages/webextension/popup.js	24.81% <0.00%> (+5.83%)	⬆️
packages/signature/index.js	72.56% <0.00%> (+6.70%)	⬆️
packages/rpc-engine/src/permissions.js	100.00% <0.00%> (+8.33%)	⬆️
packages/rpcs/eth_estimateGas/index.js	100.00% <0.00%> (+8.33%)	⬆️
packages/rpcs/cfx_call/index.js	100.00% <0.00%> (+8.51%)	⬆️
packages/rpcs/eth_chainId/index.js	100.00% <0.00%> (+9.09%)	⬆️
packages/rpcs/net_version/index.js	100.00% <0.00%> (+9.09%)	⬆️
... and 81 more

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