Complicated project : Package is not found

[drfunjohn]

go version go1.13.4 linux/amd64
GO111MODULE=on
GOPATH=/home/ubuntu/go

My project use:
go mod vendor

Tree:
MyProject
|_ db
|_pkg
| |_api
|vendor
| main.go

When I run test from root directory of project by:
mocktest -debug ./pkg/api/

I recieve next error:

.......
2019/12/12 10:31:42 installImports: label: github.com/spf13/cobra, name: github.com/spf13/cobra, mock: false
2019/12/12 10:31:42 GenPkg: srcPath:/home/ubuntu/go, dstRoot:/tmp/withmock781383690/path, name:github.com/spf13/cobra, mock:false
ERROR(AddPackage:installImports:GenPkg): Package 'github.com/spf13/cobra' not found in any of '/home/ubuntu/go'.

If I run from api directory:
cd pkg/api
withmock -debug go test

Each time random package appears in the error.

Thanx.