GoogleTest

The GoogleTest crate allows for flexible test assertions using matchers:

use googletest::prelude::*;

#[googletest::test]
fn test_elements_are() {
    let value = vec!["foo", "bar", "baz"];
    expect_that!(value, elements_are!(eq("foo"), lt("xyz"), starts_with("b")));
}

Si cambiamos el último elemento a "!", la prueba dará error y aparecerá un mensaje de error estructurado que señala cuál es el fallo:

---- test_elements_are stdout ----
Value of: value
Expected: has elements:
  0. is equal to "foo"
  1. is less than "xyz"
  2. starts with prefix "!"
Actual: ["foo", "bar", "baz"],
  where element #2 is "baz", which does not start with "!"
  at src/testing/googletest.rs:6:5
Error: See failure output above
This slide should take about 5 minutes.

  • GoogleTest no forma parte de Rust Playground, por lo que debes llevar a cabo este ejemplo en un entorno local. Usa cargo add googletest para añadirlo rápidamente a un proyecto de Cargo que ya tengas.

  • La línea use googletest::prelude::*; importa una serie de macros y tipos habituales.

  • This just scratches the surface, there are many builtin matchers. Consider going through the first chapter of "Advanced testing for Rust applications", a self-guided Rust course: it provides a guided introduction to the library, with exercises to help you get comfortable with googletest macros, its matchers and its overall philosophy.

  • A particularly nice feature is that mismatches in multi-line strings are shown as a diff:

#[test]
fn test_multiline_string_diff() {
    let haiku = "Se ha encontrado la seguridad de la memoria,\n\
 la potente escritura de Rust guía el camino,\n\
 protege el código que vayas a escribir.";
    assert_that!(
        haiku,
        eq("Se ha encontrado seguridad en la memoria,\n\
 el divertido sentido del humor de Rust guía el camino,\n\
 protege el código que vayas a escribir.")
    );
}

muestra un diff con colores (colores que no se muestran aquí):

    Value of: haiku
Expected: is equal to "Memory safety found,\nRust's silly humor guides the way,\nSecure code you'll write."
Actual: "Memory safety found,\nRust's strong typing guides the way,\nSecure code you'll write.",
  which isn't equal to "Memory safety found,\nRust's silly humor guides the way,\nSecure code you'll write."
Difference(-actual / +expected):
 Memory safety found,
-Rust's strong typing guides the way,
+Rust's silly humor guides the way,
 Secure code you'll write.
  at src/testing/googletest.rs:17:5