spectral

Fluent test assertions for Rust.

Influenced by Google Truth and other fluent assertion frameworks.

Usage

Add this to your Cargo.toml:

[dependencies]
spectral = "0.6.0"

Then add this to your crate:

extern crate spectral

To quickly start using assertions, simply use the prelude module in your test module:

use spectral::prelude::*;

Overview

Spectral allows you to write your assertions in a fluent manner by seperating out what you are testing with, what you are testing against and how you are asserting.

Simple asserts

For example, to test that a produced value is equal to an expected value, you would write:

assert_that(&1).is_equal_to(&1);

Or that a Vec contains a certain number of elements:

let test_vec = vec![1,2,3];
assert_that(&test_vec).has_length(3);

The methods avaliable for asserting depend upon the type under test and what traits are implemented.

As described below, it's recommended to use the macro form of assert_that! to provide correct file and line numbers for failing assertions.

Failure messages

For failing assertions, the usual panic message follows the following format:

    expected: <2>
     but was: <1>

To add additional clarification to the panic message, you can also deliberately state what you are asserting by calling the asserting(...) function rather than assert_that(...):

asserting(&"test condition").that(&1).is_equal_to(&2);

Which will produce:

    test condition:
    expected: <2>
     but was: <1>

Using the macro form of assert_that! will provide you with the file and line of the failing assertion as well:

    expected: vec to have length <2>
     but was: <1>

    at location: tests/parser.rs:112

Named Subjects

To make it more obvious what your subject actually is, you can call .named(...) after assert_that (or asserting(...).that(...)), which will print out the provided &str as the subject name if the assertion fails.

assert_that(&thing.attributes).named(&"thing attributes").has_length(2);

On failure, this will display:

    for subject [thing attributes]
    expected: vec to have length <2>
     but was: <1>

Mapping values

If you want to assert against a value contained within a struct, you can call map(...) with a closure, which will create a new Spec based upon the return value of the closure. You can then call any applicable assertions against the mapped value.

let test_struct = TestStruct { value: 5 };
assert_that(&test_struct).map(|val| &val.value).is_equal_to(&5);

Macros

If you add #[macro_use] to the extern crate declaration, you can also use the macro form of assert_that and asserting.

assert_that!(test_vec).has_length(5)

This allows you to pass through a subject to test without needing to deliberately turn it into a reference. However, for consistency, you can also use a deliberate reference in the macro as well.

assert_that!(&test_vec).has_length(5)

Additionally, this will provide you with the file and line number of the failing assertion (rather than just the internal spectral panic location).

Assertions (Basic)

Note: Descriptions and examples for each of the assertions are further down in this readme.

General

is_equal_to

is_not_equal_to

matches

Booleans

is_true

is_false

Numbers

is_less_than

is_less_than_or_equal_to

is_greater_than

is_greater_than_or_equal_to

Floats (optional)

is_close_to

Options

is_some -> (returns a new Spec with the Option value)

is_none

contains_value

Paths

exists

does_not_exist

is_a_file

is_a_directory

has_file_name

Results

is_ok -> (returns a new Spec with the Ok value)

is_err -> (returns a new Spec with the Err value)

is_ok_containing

is_err_containing

Strings

starts_with

ends_with

contains

Vectors

has_length

is_empty

HashMaps

has_length

is_empty

contains_key -> (returns a new Spec with the key value)

does_not_contain_key

contains_entry

does_not_contain_entry

IntoIterator/Iterator

contains

does_not_contain

contains_all_of

mapped_contains

equals_iterator

IntoIterator

matching_contains

Optional Features

Num Crate

The num crate is used for Float assertions. This feature will be enabled by default, but if you don't want the dependency on num, then simply disable it.

Assertions (Detailed)

As a general note, any type under test will usually need to implement at least Debug. Other assertions will have varying bounds attached to them.

General

is_equal_to

Asserts that the subject and the expected value are equal. The subject type must implement PartialEq.

Example

assert_that(&"hello").is_equal_to(&"hello");

Failure Message

	expected: <2>
	 but was: <1>

is_not_equal_to

Asserts that the subject and the expected value are not equal. The subject type must implement PartialEq.

Example

assert_that(&"hello").is_not_equal_to(&"hello");

Failure Message

	expected: <1> to not equal <1>
	 but was: equal

matches

Accepts a function accepting the subject type which returns a bool. Returning false will cause the assertion to fail.

NOTE: The resultant panic message will only state the actual value. It's recommended that you write your own assertions rather than relying upon this.

Example

assert_that(&"Hello").matches(|val| val.eq(&"Hello"));

Failure Message

	expectation failed for value <"Hello">

Booleans

is_true

Asserts that the subject is true. The subject type must be bool.

Example

assert_that(&true).is_true(); 

Failure Message

	expected: bool to be <true>
	 but was: <false>

is_false

Asserts that the subject is false. The subject type must be bool.

Example

assert_that(&false).is_false();

Failure Message

	expected: bool to be <false>
	 but was: <true>

Numbers

is_less_than

Asserts that the subject value is less than the expected value. The subject type must implement PartialOrd.

Example

assert_that(&1).is_less_than(&2);

Failure Message

	expected: value less than <2>
	 but was: <3>

is_less_than_or_equal_to

Asserts that the subject is less than or equal to the expected value. The subject type must implement PartialOrd.

Example

assert_that(&2).is_less_than_or_equal_to(&2);

Failure Message

	expected: value less than or equal to <2>
	 but was: <3>

is_greater_than

Asserts that the subject is greater than the expected value. The subject type must implement PartialOrd.

Example

assert_that(&2).is_greater_than(&1);

Failure Message

	expected: value greater than <3>
	 but was: <2>

is_greater_than_or_equal_to

Asserts that the subject is greater than or equal to the expected value. The subject type must implement PartialOrd.

Example

assert_that(&2).is_greater_than_or_equal_to(&1); 

Failure Message

	expected: value greater than or equal to <3>
	 but was: <2>

Floats (optional)

is_close_to

Asserts that the subject is close to the expected value by the specified tolerance. The subject type must implement Float and Debug.

Example

assert_that(&2.0f64).is_close_to(2.0f64, 0.01f64);

Failure Message

	expected: float close to <1> (tolerance of <0.01>)
	 but was: <2>

Options

is_some -> (returns a new Spec with the Option value)

Asserts that the subject is Some. The subject type must be an Option.

This will return a new Spec containing the unwrapped value if it is Some.

Example

assert_that(&Some(1)).is_some();

Chaining

assert_that(&option).is_some().is_equal_to(&"Hello");

Failure Message

	expected: option[some]
	 but was: option[none]

is_none

Asserts that the subject is None. The value type must be an Option.

Example

assert_that(&Option::None::<String>).is_none();

Failure Message

	expected: option[none]
	 but was: option<"Hello">

contains_value

Asserts that the subject is a Some containing the expected value. The subject type must be an Option.

Example

assert_that(&Some(1)).contains_value(&1);

Failure Message

	expected: option to contain <"Hi">
	 but was: <"Hello">

Paths

exists

Asserts that the subject Path or PathBuf refers to an existing location.

Example

assert_that(&Path::new("/tmp/file")).exists();

Failure Message

	expected: Path of <"/tmp/file"> to exist
	 but was: a non-existent Path

does_not_exist

Asserts that the subject Path or PathBuf does not refer to an existing location.

Example

assert_that(&Path::new("/tmp/file")).does_not_exist();

Failure Message

	expected: Path of <"/tmp/file"> to not exist
     but was: a resolvable Path

is_a_file

Asserts that the subject Path or PathBuf refers to an existing file.

Example

assert_that(&Path::new("/tmp/file")).is_a_file();

Failure Message

	expected: Path of <"/tmp/file"> to be a file
	 but was: not a resolvable file

is_a_directory

Asserts that the subject Path or PathBuf refers to an existing directory.

Example

assert_that(&Path::new("/tmp/dir/")).is_a_directory();

Failure Message

	expected: Path of <"/tmp/dir/"> to be a directory
	 but was: not a resolvable directory

has_file_name

Asserts that the subject Path or PathBuf has the expected file name.

Example

assert_that(&Path::new("/tmp/file")).has_file_name(&"file");

Failure Message

	expected: Path with file name of <pom.xml>
	 but was: <Cargo.toml>

Results

is_ok -> (returns a new Spec with the Ok value)

Asserts that the subject is Ok. The value type must be a Result.

This will return a new Spec containing the unwrapped value if it is Ok.

Example

assert_that(&Result::Ok::<usize, usize>(1)).is_ok();

Chaining

let result: Result<&str, &str> = Ok("Hello");
assert_that(&result).is_ok().is_equal_to(&"Hello");

Failure Message

	expected: result[ok]
	 but was: result[error]<"Oh no">

is_err -> (returns a new Spec with the Err value)

Asserts that the subject is Err. The value type must be a Result.

This will return a new Spec containing the unwrapped value if it is Err.

Note: This used to be called is_error, but has been renamed to match standard Rust naming.

Example

assert_that(&Result::Err::<usize, usize>(1)).is_err();

Chaining

let result: Result<&str, &str> = Err("Hello");
assert_that(&result).is_err().is_equal_to(&"Hello");

Failure Message

	expected: result[error]
	 but was: result[ok]<"Hello">

is_ok_containing

Asserts that the subject is an Ok Result containing the expected value. The subject type must be a Result.

Example

assert_that(&Result::Ok::<usize, usize>(1)).is_ok_containing(&1);

Failure Message

	expected: Result[ok] containing <"Hi">
	 but was: Result[ok] containing <"Hello">

is_err_containing

Asserts that the subject is an Err Result containing the expected value. The subject type must be a Result.

Example

assert_that(&Result::Err::<usize, usize>(1)).is_err_containing(&1);

Failure Message

	expected: Result[err] containing <"Oh no">
	 but was: Result[err] containing <"Whoops">

Strings

starts_with

Asserts that the subject &str or String starts with the provided &str.

Example

assert_that(&"Hello").starts_with(&"H");

Failure Message

	expected: string starting with <"A">
	 but was: <"Hello">

ends_with

Asserts that the subject &str or String ends with the provided &str.

Example

assert_that(&"Hello").ends_with(&"o");

Failure Message

	expected: string ending with <"A">
	 but was: <"Hello">

contains

Asserts that the subject &str or String contains the provided &str.

Example

assert_that(&"Hello").contains(&"e");

Failure Message

	expected: string containing <"A">
	 but was: <"Hello">

Vectors

has_length

Asserts that the length of the subject vector is equal to the provided length. The subject type must be of Vec.

Example

assert_that(&vec![1, 2, 3, 4]).has_length(4);

Failure Message

	expected: vec to have length <1>
	 but was: <3>

is_empty

Asserts that the subject vector is empty. The subject type must be of Vec.

Example

let test_vec: Vec<u8> = vec![];
assert_that(&test_vec).is_empty();

Failure Message

	expected: an empty vec
	 but was: a vec with length <1>

HashMaps

has_length

Asserts that the length of the subject hashmap is equal to the provided length. The subject type must be of HashMap.

Example

let mut test_map = HashMap::new();
test_map.insert(1, 1);
test_map.insert(2, 2);

assert_that(&test_map).has_length(2);

Failure Message

	expected: hashmap to have length <1>
	 but was: <2>

is_empty

Asserts that the subject hashmap is empty. The subject type must be of HashMap.

Example

let test_map: HashMap<u8, u8> = HashMap::new();
assert_that(&test_map).is_empty();

Failure Message

	expected: an empty hashmap
	 but was: a hashmap with length <1>

contains_key -> (returns a new Spec with the key value)

Asserts that the subject hashmap contains the expected key. The subject type must be of HashMap.

This will return a new Spec containing the associated value if the key is present.

Example

let mut test_map = HashMap::new();
test_map.insert("hello", "hi");

assert_that(&test_map).contains_key(&"hello");

Chaining

let mut test_map = HashMap::new();
test_map.insert("hello", "hi");

assert_that(&test_map).contains_key(&"hello").is_equal_to(&"hi");

Failure Message

	expected: hashmap to contain key <"hello">
	 but was: <["hey", "hi"]>

does_not_contain_key

Asserts that the subject hashmap does not contain the provided key. The subject type must be of HashMap.

Example

let mut test_map = HashMap::new();
test_map.insert("hello", "hi");

assert_that(&test_map).does_not_contain_key(&"hey");

Failure Message

	expected: hashmap to not contain key <"hello">
	 but was: present in hashmap

contains_entry

Asserts that the subject hashmap contains the expected key with the expected value. The subject type must be of HashMap.

Example

let mut test_map = HashMap::new();
test_map.insert("hello", "hi");

assert_that(&test_map).contains_entry(&"hello", &"hi");

Failure Message

    expected: hashmap containing key <"hi"> with value <"hey">
     but was: key <"hi"> with value <"hello"> instead

does_not_contain_entry

Asserts that the subject hashmap does not contain the provided key and value. The subject type must be of HashMap.

Example

let mut test_map = HashMap::new();
test_map.insert("hello", "hi");

assert_that(&test_map).does_not_contain_entry(&"hello", &"hey");

Failure Message

    expected: hashmap to not contain key <"hello"> with value <"hi">
     but was: present in hashmap

IntoIterator/Iterator

contains

Asserts that the subject contains the provided value. The subject must implement IntoIterator or Iterator, and the contained type must implement PartialEq and Debug.

Example

let test_vec = vec![1,2,3];
assert_that(&test_vec).contains(&2);

Failure Message

	expected: iterator to contain <1>
	 but was: <[5, 6]>

does_not_contain

Asserts that the subject does not contain the provided value. The subject must implement IntoIterator or Iterator, and the contained type must implement PartialEq and Debug.

Example

let test_vec = vec![1,2,3];
assert_that(&test_vec).does_not_contain(&4);

Failure Message

	expected: iterator to not contain <1>
	 but was: <[1, 2]>

contains_all_of

Asserts that the subject contains all of the provided values. The subject must implement IntoIterator or Iterator, and the contained type must implement PartialEq and Debug.

Example

let test_vec = vec![1, 2, 3];
assert_that(&test_vec.iter()).contains_all_of(&vec![&2, &3]);

Failure Message

    expected: iterator to contain items <[1, 6]>
     but was: <[1, 2, 3]>

mapped_contains

Maps the values of the subject before asserting that the mapped subject contains the provided value. The subject must implement IntoIterator, and the type of the mapped value must implement PartialEq.

NOTE: The panic message will refer to the mapped values rather than the values present in the original subject.

Example

#[derive(PartialEq, Debug)]
struct Simple {
    pub val: usize,
}

...

assert_that(&vec![Simple { val: 1 }, Simple { val: 2 } ]).mapped_contains(|x| &x.val, &2);

Failure Message

	expected: iterator to contain <5>
	 but was: <[1, 2, 3]>

equals_iterator

Asserts that the subject is equal to provided iterator. The subject must implement IntoIterator or Iterator, the contained type must implement PartialEq and Debug and the expected value must implement Iterator and Clone.

Example

let expected_vec = vec![1,2,3];
let test_vec = vec![1,2,3];
assert_that(&test_vec).equals_iterator(&expected_vec.iter());

Failure Message

	expected: Iterator item of <4> (read <[1, 2]>)
	 but was: Iterator item of <3> (read <[1, 2]>)

IntoIterator

matching_contains

Asserts that the subject contains a matching item by using the provided function. The subject must implement IntoIterator, and the contained type must implement Debug.

Example

let mut test_into_iter = LinkedList::new();
test_into_iter.push_back(TestEnum::Bad);
test_into_iter.push_back(TestEnum::Good);
test_into_iter.push_back(TestEnum::Bad);

assert_that(&test_into_iter).matching_contains(|val| {
    match val {
        &TestEnum::Good => true,
        _ => false
    }
});

Failure Message

expectation failed for iterator with values <[Bad, Bad, Bad]>

How it works

The Spec struct implements a number of different bounded traits which provide assertions based upon the bound type.

As a single example, length assertions are provided by the VecAssertions trait:

pub trait VecAssertions {            
    fn has_length(self, expected: usize);
} 

Which is then implemented by Spec:

impl<'s, T> VecAssertions for Spec<'s, Vec<T>> {
    fn has_length(self, expected: usize) {
      ...
    }
} 

Naturally traits need to be included with a use before they apply, but to avoid an excessive number of use statements there is a prelude module which re-exports commonly used assertion traits.

Creating your own

To create your own assertions, simply create a new trait containing your assertion methods and implement Spec against it.

To fail an assertion, create a new AssertionFailure struct using from_spec(...) within your assertion method and pass in self.

AssertionFailure also implements builder methods with_expected(...), with_actual(...) and fail(...), which provides the necessary functionality to fail the test with the usual message format. If you need greater control of the failure message, you can call fail_with_message(...) which will directly print the provided message.

In either case, any description provided using asserting(...) will always be prepended to the panic message.

For example, to create an assertion that the length of a Vec is at least a certain value:

trait VecAtLeastLength {
    fn has_at_least_length(&mut self, expected: usize);
}

impl<'s, T> VecAtLeastLength for Spec<'s, Vec<T>> {
    fn has_at_least_length(&mut self, expected: usize) {
        let subject = self.subject;
        if expected > subject.len() {
            AssertionFailure::from_spec(self)
                .with_expected(format!("vec with length at least <{}>", expected))
                .with_actual(format!("<{}>", subject.len()))
                .fail();
        }
    }
}