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catch-and-match
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Assert an error thrown (a)synchronously by a function.
Made with ❤ at @outlandish
npm install catch-and-match --save-dev
Sometimes asserting that something just throws isn't enough. catch-and-match
allows you to assert that a function
which should throw throws the error you expect. This is particularly useful for testing functions that produce error
messages which provide useful feedback (the best kind of functions!).
Assert error is an instance of Error (e.g. ReferenceError)
Replace a traditional try/catch
it('should throw a ReferenceError', function (cb) {
// Without catch-and-match | // With catch-and-match
try { | catchAndMatch(
String(a); // a === undefined | () => String(a),
} catch (err) { | ReferenceError,
if (!(err instanceof ReferenceError)) { | cb);
cb(new Error()); |
return; | // Or return a Promise
} | return catchAndMatch(
cb(); | () => String(a),
} | ReferenceError);
});
Replace catching a rejected Promise
it('should throw a ReferenceError', function () {
// Without catch-and-match | // With catch-and-match
return someFuncThatRejects() | catchAndMatch(
.catch((err) => { | someFuncThatRejects,
if (!(err instanceof ReferenceError)) { | ReferenceError);
throw err; |
} |
}); |
});
Assert error message using a regular expression
it('should throw with error message containing "not defined"', function (cb) {
return catchAndMatch(() => String(a), /not defined/);
});
Assert error message using a string
it('should throw with error message "a is not defined"', function (cb) {
return catchAndMatch(() => String(a), 'a is not defined');
});
Assert error matches custom validation
it('should throw with error message "a is not defined"', function (cb) {
return catchAndMatch(() => String(a), function (err) {
return err.message === 'a is not defined';
});
});
catchAndMatch(fn, matcher[, cb]) : Promise
fn {Function} function that should throw traditionally or within a Promise
fn
does not throw, catch-and-match
returns a rejected Promise and calls cb
with an error as its first argumentfn
throws the error is tested against matcher
(see below)matcher {RegExp|String|Function|Error} method of inspecting error:
new RegExp(str)
)re.test(err.message)
)Error
) is matched against the error (e.g. err.constructor === ReferenceError
)cb {Function} (optional) error-first callback
If in your tests you are placing function invocations within a try
block to purposefully cause them to throw and then
calling the test's 'done' callback within the catch
after inspecting the error, you can replace this pattern with a
catchAndMatch
:
Example function
function log (str) {
if (typeof str !== 'string') {
throw new Error('str should be a string');
}
console.log(str);
}
Before
it('should throw an error without correct arguments', function (cb) {
try {
// make the function throw by passing an illegal argument
log(10);
} catch (err) {
// inspect that the error thrown has the right message
if (err.message.includes('should be a string')) {
cb();
return;
}
// the wrong error was thrown, so fail the test
cb(new Error('wrong error thrown'));
}
});
After, using Promise
// Passes with string matcher
it('should throw an error without correct arguments', function () {
return catchAndMatch(log.bind(undefined, 'hello'), /should be a string/);
});
// Passes with function matcher
it('should throw an error without correct arguments', function () {
return catchAndMatch(log.bind(undefined, 10), function (err) {
return err.includes('should be a string');
});
});
After, using callback
// Fails with RegExp matcher
it('should throw an error without correct arguments', function (cb) {
catchAndMatch(log.bind(undefined, 10), /should be a string/, cb);
});
All pull requests and issues welcome! If you're not sure how, check out Kent C. Dodds' great video tutorials on egghead.io!
FAQs
Assert an error thrown (a)synchronously by a function.
The npm package catch-and-match receives a total of 25 weekly downloads. As such, catch-and-match popularity was classified as not popular.
We found that catch-and-match 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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