How do I import my main crate into my test files? Rust doc example doesn't work

Question

I'm setting up unit tests for my rust project and using this guide. The documentation says to do something like this, where "adder" is the project name (if I am not mistaken).

tests/integration_test.rs

use adder;
mod common;

#[test]
fn it_adds_two() {
    common::setup();
    assert_eq!(4, adder::add_two(2));
}

I've done something similar. My folder structure is tests/users.rs where tests/ is right next to src/ as in the example. Here is what my test file actually looks like:

tests/users.rs

use test_project;

#[test]
pub fn create_test() {
    //do things with the modules from main 
}

But I'm getting this error: no external crate 'test_project'

As far as I can tell I'm following the documentation to the letter. Can someone point out what I could be missing here?

Here is my folder structure also:

I have no problems running a dummy test without the imports cargo test so cargo is able to find the tests/ folder without any issues

Here is my Cargo.toml

[package]
name = "test_project"
version = "0.1.0"
authors = ["mcrandall <[email protected]>"]
edition = "2018"

[lib]
name = "errormsg"
path = "errormsg/src/lib.rs"

[dependencies]
diesel = { version = "1.4.5", features = ["sqlite"] }
dotenv = "0.15.0"
download_rs = "0.2.0"
futures = "0.3.12"
futures-util = "0.3.12"
oauth2 = { version = "3.0"}
reqwest = { version = "0.11", features = ["json", "stream", "blocking"] }
serde = { version= "1.0.123", features = ["derive"] }
serde_derive = "1.0.123"
serde_json = "1.0.61"
simple-server = "0.4.0"
tokio = { version = "1", features = ["full"] }
url = "2.2.0"
uuid = { version = "0.8.2", features = ["v4"] }

Answer 1

Make sure that in your Cargo.toml name = "test_project". Also, you can only import it if it is a library Library Documentation.

Looking at your Cargo.toml, the lib section tells cargo that this package exports one lib called errormsg contained in errormsg/src/lib.rs. So test_project will not be available for you, because only one lib is allowed per package why?.

There are two solutions to your problem.
You can either make errormsg a module which you then can import for example with test_project::errormsg in tests/users.rs.
Or you can create a separate package and then import it in the Cargo.toml file:

[dependencies]
errormsg = { version = "0.1", path = "./../errormsg" }

Another way is to use workspaces to group packages, but i'm not really familiar with it.