When writing unit tests which loads some "fixture" from a file, e.g. a .json file it is incredible helpful to use include_str! to assert at compile time that the file exists. However, it increases the size of the test binary, right? so maybe that is not wanted.

I want a macro which checks for the presence of a file at compile time, but I want to load the actual contents of the file at runtime. I think no such macro exists to day?

And I want to to this inline in my unit test, i.e. no build script.

So I wanted to check if other would find this useful? Maybe called file_exists

Actually it would be neat with another macro - read_file! which would use file_exists! at compile time and use fs::read_to_string at runtime:

1. at compile time checks for the existence of the file
2. at runtime loads it contents

#[test]
fn test_deserialize_user()  {
    // This verifies the existince of the file at compile time, and reads its contents at runtime.
    let fixture = read_file!("user.json"); 
    let deserialization_result = serde_json::from_str(fixture)
    assert!(deserialization_result.is_ok());
}

is that possible - if written part of std? Would anyone else beside me find it useful?

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