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Rich matchers inspired by Hamcrest. Useful for generating helpful assertion failure messages in tests.
duck.js allows you to perform assertions on complex objects. When those assertions fail, duck.js will try to produce helpful error messages. For instance, suppose you want to assert the same property on an array of objects:
var duck = require("duck");
var isArray = duck.isArray;
var hasProperties = duck.hasProperties;
var users = fetchUsers();
duck.assertThat(users, isArray([
hasProperties({name: "Bob"}),
hasProperties({name: "Jim"}),
]));
which might produce an error message like:
Expected [object with properties {
name: 'Bob'
}, object with properties {
name: 'Jim'
}]
but element at index 0 didn't match:
value of property "name" didn't match:
was 'Jim'
expected 'Bob'
expected object with properties {
name: 'Bob'
}
element at index 1 didn't match:
value of property "name" didn't match:
was 'Bob'
expected 'Jim'
expected object with properties {
name: 'Jim'
}
The below is a quick reference to the API. For more examples, take a look at the tests.
Assert that value
satifies matcher
.
If value
satifies matcher
, return normally, otherwise throw an
AssertionError describing the mismatch.
If value
is a matcher, return that matcher,
otherwise return duck.equalTo(value)
.
Matcher for deep equality on value
.
An object obj
matches duck.isObject(matcherObj)
if:
obj
matches duck.hasProperties(matcherObj)
, andobj
but not in matcherObj
Sample usage:
duck.isObject({
name: "Bob",
address: duck.isObject({
city: "Cambridge",
county: "UK"
})
})
duck.is
is called on each value of the matcher object, meaning that the
above is equivalent to:
duck.isObject({
name: duck.is("Bob"),
address: duck.isObject({
city: duck.is("Cambridge"),
county: duck.is("UK")
})
})
An object obj
matches duck.hasProperties(matcherProperties)
if,
for each key
in matcherProperties
, matcherProperties[key].matches(obj[key])
Sample usage:
duck.hasProperties({
name: "Bob",
address: duck.hasProperties({
city: "Cambridge",
county: "UK"
})
})
duck.is
is called on each value of the matcher object, meaning that the
above is equivalent to:
duck.hasProperties({
name: duck.is("Bob"),
address: duck.hasProperties({
city: duck.is("Cambridge"),
county: duck.is("UK")
})
})
An array blah
matches duck.isArray(matcherArray)
if:
blah.length == matcherArray.length
, and0 <= i < array.length
, matcherArray[i].matches(blah[i])
Sample usage:
duck.isArray([
duck.hasProperties({name: "Bob"}),
duck.hasProperties({name: "Jim"}),
]))
duck.is
is called on each element of the matcher array, meaning that the
following are equivalent:
duck.isArray(["apple", "banana"])
duck.isArray([duck.is("apple"), duck.is("banana")])
Each matcher has the following methods:
Return true
if value
satifies this matcher, false otherwise.
Generate a string describing why value
doesn't satisfy this matcher.
Behaviour is undefined if value
actually satisifies the matcher.
Equivalent to:
var isMatch = this.matches(value);
return {
matches: isMatch,
description: isMatch ? "" : this.describeMismatch(value)
};
Useful if you're likely to want both the boolean and the mismatch description.
Generate a string describing the matcher.
Thanks to Hamcrest for inspiration.
FAQs
Rich matchers inspired by Hamcrest. Useful for generating helpful assertion failure messages in tests.
The npm package duck receives a total of 302,232 weekly downloads. As such, duck popularity was classified as popular.
We found that duck demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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