Manage custom packages and projects - julia

Question

I'm new to Julia.
I'm seeking the best practice of structuring directories, packages, and projects.
Compared with Python, the most annoying parts in Julia are as follows:
The path for e.g. include seems depend on the path of executed file. I'd like to keep a specific reference path so that I can load some files easily.
I asked similar questions here, and someone told me that creating packages and using using will be easy to manage my projects.
However, It's really confusing when loading files and modules. For example,
MyProject
├── MyPkg1
│   ├── src
│   │   └── MyPkg1.jl
│   └── test
│   └── runtests.jl
└── MyPkg2
├── src
│   └── MyPkg1.jl
└── test
└── runtests.jl
6 directories, 4 files
a) MyPkg1/src/MyPkg1.jl
module MyPkg1
export func_export
function func_export
println("hi")
end
end
b) MyPkg1/test/runtests.jl
using MyPkg1
using Test
#testset "MyPkg1.jl" begin
func_export() # raise error: func_export not defined
end
c) MyPkg2/test/runtests.jl
using MyPkg2
using Test
using MyPkg1 # other Pkg
#testset "MyPkg2.jl" begin
func_export() # raise error
end
As written in the above codes, some errors are raised (see b), c)).
So my questions are...
If I did something wrong in the above example, please explain why errors occur in detail.
What's the best practice in developing Julia projects in the sense of directory structure?