cargo build

% cargo build --target=thumbv6-none-eabi --verbose -j1 --lib
   Compiling core v1.0.0 (https://github.com/hackndev/rust-libcore#d9dc4f94)
     Running `rustc /Users/farcaller/.cargo/git/checkouts/rust-libcore-a3e1d25b35d5cd12/master/./build.rs --crate-name build_script_build --crate-type bin -C prefer-dynamic -g --out-dir /Users/farcaller/temp/bug/test/target/debug/build/core-59996a419f60f2f9 --emit=dep-info,link -L dependency=/Users/farcaller/temp/bug/test/target/debug/deps -L dependency=/Users/farcaller/temp/bug/test/target/debug/deps -Awarnings`
       Fresh libc v0.1.8
       Fresh rustc-serialize v0.3.15
       Fresh rand v0.3.8
       Fresh num v0.1.25
       Fresh expectest v0.2.1
     Running `/Users/farcaller/temp/bug/test/target/debug/build/core-59996a419f60f2f9/build-script-build`
     Running `rustc /Users/farcaller/.cargo/git/checkouts/rust-libcore-a3e1d25b35d5cd12/master/rust/src/libcore/lib.rs --crate-name core --crate-type lib -g -C metadata=59996a419f60f2f9 -C extra-filename=-59996a419f60f2f9 --out-dir /Users/farcaller/temp/bug/test/target/thumbv6-none-eabi/debug/deps --emit=dep-info,link --target thumbv6-none-eabi -L dependency=/Users/farcaller/temp/bug/test/target/thumbv6-none-eabi/debug/deps -L dependency=/Users/farcaller/temp/bug/test/target/thumbv6-none-eabi/debug/deps -Awarnings`
   Compiling test v0.1.0 (file:///Users/farcaller/temp/bug/test)
     Running `rustc src/lib.rs --crate-name test --crate-type lib -g --out-dir /Users/farcaller/temp/bug/test/target/thumbv6-none-eabi/debug --emit=dep-info,link --target thumbv6-none-eabi -L dependency=/Users/farcaller/temp/bug/test/target/thumbv6-none-eabi/debug -L dependency=/Users/farcaller/temp/bug/test/target/thumbv6-none-eabi/debug/deps --extern core=/Users/farcaller/temp/bug/test/target/thumbv6-none-eabi/debug/deps/libcore-59996a419f60f2f9.rlib`

Cargo.toml

[package]
name = "test"
version = "0.1.0"
authors = ["Vladimir Pouzanov <farcaller@gmail.com>"]

[lib]
name = "test"
crate-type = ["lib"]

[target.thumbv6-none-eabi.dependencies.core]
git = "https://github.com/hackndev/rust-libcore"

[dev-dependencies]
expectest = "*"

src-lib.rs

#![feature(no_std, core)]

#![no_std]

extern crate core;

#[cfg(test)] extern crate std;

#[cfg(test)] #[macro_use(expect)] extern crate expectest;

fn f() -> u8 {
    42
}

#[test]
fn it_works() {
    use expectest::prelude::*;

    let v = f();
    // expect!(v).to(be_equal_to(42));
    expect(v)
        .location(expectest::core::SourceLocation::new(file!(), line!()))
        .to(be_equal_to(42));
}