Getting Started

These exercises lean on Test-Driven Development (TDD), but they're not an exact match.

The following steps assume that you are in the same directory as the exercise.

You must have Rust installed. Follow the Installation chapter in the Rust book. The Rust language section section from exercism is also useful.

Step 1

Run the test suite. It can be run with cargo, which is installed with Rust.

$ cargo test

This will compile the hello-world crate and run the test, which fails.

running 1 test
test hello_world ... FAILED

failures:

---- hello_world stdout ----
thread 'hello_world' panicked at 'assertion failed: `(left == right)`
(left: `"Hello, World!"`, right: `"Goodbye, Mars!"`)', tests/hello-world.rs:5

failures:
    hello_world

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured

Understanding Test Failures

The hello_world failure states that it is expecting the value, "Hello, World!", to be returned from hello(). The left side of the assertion (at line 5) should be equal to the right side.

---- hello_world stdout ----
thread 'hello_world' panicked at 'assertion failed: `(left == right)`
(left: `"Hello, World!"`, right: `"Goodbye, Mars!"`)', tests/hello-world.rs:5

Fixing the Error

To fix it, open up src/lib.rs and change the hello function to return "Hello, World!" instead of "Goodbye, Mars!".

pub fn hello() -> &'static str {
    "Hello, World!"
}

Step 2

Run the test again. This time, it will pass.

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured

     Running target/debug/deps/hello_world-bd1f06dc726ef14f

running 1 test
test hello_world ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured

   Doc-tests hello-world

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured

Submit

Once the test is passing, you can submit your code with the following command:

$ exercism submit

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