Error: Cannot create instance of IERC20; no code at address

[yuzhongrong]

why？

Everything is up to date, there is nothing to compile.

Contract: TestDyDxSoloMargin
1) "before each" hook for "flash loan"

0 passing (1s)
1 failing

1. Contract: TestDyDxSoloMargin
   "before each" hook for "flash loan":
   Error: Cannot create instance of IERC20; no code at address 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48
   at Object.checkCode (node_modules/truffle/build/webpack:/packages/contract/lib/utils/index.js:263:1)
   at Function.at (node_modules/truffle/build/webpack:/packages/contract/lib/contract/constructorMethods.js:73:1)
   at processTicksAndRejections (internal/process/task_queues.js:97:5)
   at Context. (test/test-dydx-solo-margin.js:20:13)