I want to write unit tests in golang for a struct which accepts an io.Reader in the constructor. Usually the io.Reader interface is coming from a TCP connection.

Now I want to use a predefined string and use this as input to the io.Reader interface.

Something like:

```
s := "this is my input"
b := io.NewReader(s)
t := NewTestStruct(b)
t.doSomething()

```