Crate googletest

Expand description

A rich test assertion library for Rust.

This library provides:

A framework for writing matchers which can be combined to make a wide range of assertions on data,
A rich set of matchers, and
A new set of test assertion macros.

Assertions and matchers

The core of GoogleTest is its matchers. Matchers indicate what aspect of an actual value one is asserting: (in-)equality, containment, regular expression matching, and so on.

To make an assertion using a matcher, GoogleTest offers three macros:

assert_that! panics if the assertion fails, aborting the test.
expect_that! logs an assertion failure, marking the test as having failed, but allows the test to continue running (called a non-fatal assertion). It requires the use of the googletest::test attribute macro on the test itself.
verify_that! has no side effects and evaluates to a Result whose Err variant describes the assertion failure, if there is one. In combination with the ? operator, this can be used to abort the test on assertion failure without panicking. It is also the building block for the other two macros above.

For example:

use googletest::prelude::*;

#[test]
fn fails_and_panics() {
    let value = 2;
    assert_that!(value, eq(4));
}

#[googletest::test]
fn two_logged_failures() {
    let value = 2;
    expect_that!(value, eq(4)); // Test now failed, but continues executing.
    expect_that!(value, eq(5)); // Second failure is also logged.
}

#[test]
fn fails_immediately_without_panic() -> Result<()> {
    let value = 2;
    verify_that!(value, eq(4))?; // Test fails and aborts.
    verify_that!(value, eq(2))?; // Never executes.
    Ok(())
}

#[test]
fn simple_assertion() -> Result<()> {
    let value = 2;
    verify_that!(value, eq(4)) // One can also just return the last assertion.
}

Matchers are composable:

use googletest::prelude::*;

#[googletest::test]
fn contains_at_least_one_item_at_least_3() {
    let value = vec![1, 2, 3];
    expect_that!(value, contains(ge(3)));
}

They can also be logically combined:

use googletest::prelude::*;

#[googletest::test]
fn strictly_between_9_and_11() {
    let value = 10;
    expect_that!(value, gt(9).and(not(ge(11))));
}

Available matchers

The following matchers are provided in GoogleTest Rust:

Matcher	What it matches
`all!`	Anything matched by all given matchers.
`any!`	Anything matched by at least one of the given matchers.
`anything`	Any input.
`approx_eq`	A floating point number within a standard tolerance of the argument.
`char_count`	A string with a Unicode scalar count matching the argument.
`container_eq`	Same as `eq`, but for containers (with a better mismatch description).
`contains`	A container containing an element matched by the given matcher.
`contains_each!`	A container containing distinct elements each of the arguments match.
`contains_regex`	A string containing a substring matching the given regular expression.
`contains_substring`	A string containing the given substring.
`displays_as`	A `Display` value whose formatted string is matched by the argument.
`each`	A container all of whose elements the given argument matches.
`elements_are!`	A container whose elements the arguments match, in order.
`empty`	An empty collection.
`ends_with`	A string ending with the given suffix.
`eq`	A value equal to the argument, in the sense of the `PartialEq` trait.
`eq_deref_of`	A value equal to the dereferenced value of the argument.
`err`	A `Result` containing an `Err` variant the argument matches.
`field!`	A struct or enum with a given field whose value the argument matches.
`ge`	A `PartialOrd` value greater than or equal to the given value.
`gt`	A `PartialOrd` value strictly greater than the given value.
`has_entry`	A `HashMap` containing a given key whose value the argument matches.
`is_contained_in!`	A container each of whose elements is matched by some given matcher.
`is_nan`	A floating point number which is NaN.
`le`	A `PartialOrd` value less than or equal to the given value.
`len`	A container whose number of elements the argument matches.
`lt`	A `PartialOrd` value strictly less than the given value.
`matches_pattern!`	A struct or enum whose fields are matched according to the arguments.
`matches_regex`	A string matched by the given regular expression.
`near`	A floating point number within a given tolerance of the argument.
`none`	An `Option` containing `None`.
`not`	Any value the argument does not match.
`ok`	A `Result` containing an `Ok` variant the argument matches.
`pat!`	Alias for `matches_pattern!`.
`points_to`	Any `Deref` such as `&`, `Rc`, etc. whose value the argument matches.
`pointwise!`	A container whose contents the arguments match in a pointwise fashion.
`predicate`	A value on which the given predicate returns true.
`some`	An `Option` containing `Some` whose value the argument matches.
`starts_with`	A string starting with the given prefix.
`subset_of`	A container all of whose elements are contained in the argument.
`superset_of`	A container containing all elements of the argument.
`unordered_elements_are!`	A container whose elements the arguments match, in any order.

Writing matchers

One can extend the library by writing additional matchers. To do so, create a struct holding the matcher’s data and have it implement the trait Matcher:

use googletest::{description::Description, matcher::{Matcher, MatcherResult}};
use std::fmt::Debug;

struct MyEqMatcher<T> {
    expected: T,
}

impl<T: PartialEq + Debug> Matcher for MyEqMatcher<T> {
    type ActualT = T;

    fn matches(&self, actual: &Self::ActualT) -> MatcherResult {
        if self.expected == *actual {
            MatcherResult::Match
        } else {
            MatcherResult::NoMatch
        }
    }

    fn describe(&self, matcher_result: MatcherResult) -> Description {
        match matcher_result {
            MatcherResult::Match => {
                format!("is equal to {:?} the way I define it", self.expected).into()
            }
            MatcherResult::NoMatch => {
                format!("isn't equal to {:?} the way I define it", self.expected).into()
            }
        }
    }
}

It is recommended to expose a function which constructs the matcher:

pub fn eq_my_way<T: PartialEq + Debug>(expected: T) -> impl Matcher<ActualT = T> {
   MyEqMatcher { expected }
}

The new matcher can then be used in the assertion macros:

#[googletest::test]
fn should_be_equal_by_my_definition() {
    expect_that!(10, eq_my_way(10));
}

Using non-fatal assertions, a single test is able to log multiple assertion failures. Any single assertion failure causes the test to be considered having failed, but execution continues until the test completes or otherwise aborts.

To make a non-fatal assertion, use the macro expect_that!. The test must also be marked with googletest::test instead of the Rust-standard #[test].

use googletest::prelude::*;

#[googletest::test]
fn three_non_fatal_assertions() {
    let value = 2;
    expect_that!(value, eq(2));  // Passes; test still considered passing.
    expect_that!(value, eq(3));  // Fails; logs failure and marks the test failed.
    expect_that!(value, eq(4));  // A second failure, also logged.
}

This can be used in the same tests as verify_that!, in which case the test function must also return [Result<()>]:

use googletest::prelude::*;

#[googletest::test]
fn failing_non_fatal_assertion() -> Result<()> {
    let value = 2;
    expect_that!(value, eq(3));  // Just marks the test as having failed.
    verify_that!(value, eq(2))?;  // Passes, so does not abort the test.
    Ok(())        // Because of the failing expect_that! call above, the
                  // test fails despite returning Ok(())
}

use googletest::prelude::*;

#[googletest::test]
fn failing_fatal_assertion_after_non_fatal_assertion() -> Result<()> {
    let value = 2;
    expect_that!(value, eq(2));  // Passes; test still considered passing.
    verify_that!(value, eq(3))?; // Fails and aborts the test.
    expect_that!(value, eq(3));  // Never executes, since the test already aborted.
    Ok(())
}

Predicate assertions

The macro verify_pred! provides predicate assertions analogous to GoogleTest’s EXPECT_PRED family of macros. Wrap an invocation of a predicate in a verify_pred! invocation to turn that into a test assertion which passes precisely when the predicate returns true:

fn stuff_is_correct(x: i32, y: i32) -> bool {
    x == y
}

let x = 3;
let y = 4;
verify_pred!(stuff_is_correct(x, y))?;

The assertion failure message shows the arguments and the values to which they evaluate:

stuff_is_correct(x, y) was false with
  x = 3,
  y = 4

The verify_pred! invocation evaluates to a [Result<()>] just like verify_that!. There is also a macro expect_pred! to make a non-fatal predicaticate assertion.

Unconditionally generating a test failure

The macro fail! unconditionally evaluates to a Result indicating a test failure. It can be used analogously to verify_that! and verify_pred! to cause a test to fail, with an optional formatted message:

#[test]
fn always_fails() -> Result<()> {
    fail!("This test must fail with {}", "today")
}

Integrations with other crates

GoogleTest Rust includes integrations with the Anyhow and Proptest crates to simplify turning errors from those crates into test failures.

To use this, activate the anyhow, respectively proptest feature in GoogleTest Rust and invoke the extension method into_test_result() on a Result value in your test. For example:

#[test]
fn has_anyhow_failure() -> Result<()> {
    Ok(just_return_error().into_test_result()?)
}

fn just_return_error() -> anyhow::Result<()> {
    anyhow::Result::Err(anyhow!("This is an error"))
}

One can convert Proptest test failures into GoogleTest test failures when the test is invoked with TestRunner::run:

#[test]
fn numbers_are_greater_than_zero() -> Result<()> {
    let mut runner = TestRunner::new(Config::default());
    runner.run(&(1..100i32), |v| Ok(verify_that!(v, gt(0))?)).into_test_result()
}

Similarly, when the proptest feature is enabled, GoogleTest assertion failures can automatically be converted into Proptest TestCaseError through the ? operator as the example above shows.

Modules

description
matcher
The components required to implement matchers.
matcher_support
Utilities to facilitate writing matchers.
matchers
All built-in matchers of this crate are in submodules of this module.
prelude
Re-exports of the symbols in this crate which are most likely to be used.

Macros

assert_pred
Asserts that the given predicate applied to the given arguments returns true, panicking if it does not.
assert_that
Matches the given value against the given matcher, panicking if it does not match.
expect_pred
Asserts that the given predicate applied to the given arguments returns true, failing the test but continuing execution if not.
expect_that
Matches the given value against the given matcher, marking the test as failed but continuing execution if it does not match.
fail
Evaluates to a Result which contains an Err variant with the given test failure message.
verify_pred
Asserts that the given predicate applied to the given arguments returns true.
verify_that
Checks whether the Matcher given by the second argument matches the first argument.

Traits

GoogleTestSupport
Adds to Result support for GoogleTest Rust functionality.
IntoTestResult
Provides an extension method for converting an arbitrary type into a Result.

Functions

verify_current_test_outcome
Returns a Result corresponding to the outcome of the currently running test.

Type Aliases

Result
A Result whose Err variant indicates a test failure.

Attribute Macros

test
Marks a test to be run by the Google Rust test runner.