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Add assert.rejects and assert.not.rejects methods for promises #132

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Add assert.rejects and assert.not.rejects methods for promises #132

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bdd8b6f
Add assert.rejects and assert.not.rejects methods for promises
aral Aug 10, 2021
f007c7e
Update src/assert.js
aral Aug 11, 2021
7a03d8c
Update src/assert.js
aral Aug 11, 2021
bbd9ba6
Update src/assert.js
aral Aug 11, 2021
74b0d02
Update src/assert.js
aral Aug 11, 2021
009b09c
Update tests based on changes from review
aral Aug 11, 2021
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38 changes: 38 additions & 0 deletions src/assert.js
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,26 @@ export function throws(blk, exp, msg) {
}
}

export async function rejects(blk, exp, msg) {
if (!msg && typeof exp === 'string') {
msg = exp; exp = null;
}

try {
await blk();
assert(false, false, true, 'rejects', false, 'Expected promise to reject', msg);
} catch (err) {
if (err instanceof Assertion) throw err;

if (typeof exp === 'function') {
assert(exp(err), false, true, 'rejects', false, 'Expected promise to reject matching exception', msg);
} else if (exp instanceof RegExp) {
const errorMessage = err instanceof Error ? err.message : err
assert(exp.test(errorMessage), false, true, 'rejects', false, `Expected promise to reject matching exception \`${String(exp)}\` pattern`, msg);
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}
}
}

// ---

export function not(val, msg) {
Expand Down Expand Up @@ -158,3 +178,21 @@ not.throws = function (blk, exp, msg) {
}
}
}

not.rejects = async function (blk, exp, msg) {
if (!msg && typeof exp === 'string') {
msg = exp; exp = null;
}

try {
await blk();
} catch (err) {
if (typeof exp === 'function') {
assert(!exp(err), true, false, 'not.rejects', false, 'Expected function not to reject promise matching exception', msg);
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} else if (exp instanceof RegExp) {
assert(!exp.test(err instanceof Error ? err.message : err), true, false, 'not.rejects', false, `Expected function not to reject promise exception matching \`${String(exp)}\` pattern`, msg);
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} else if (!exp) {
assert(false, true, false, 'not.rejects', false, 'Expected function not to reject promise', msg);
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}
}
}
171 changes: 170 additions & 1 deletion test/assert.js
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Expand Up @@ -366,6 +366,7 @@ throws('should be a function', () => {
throws('should throw if function does not throw Error :: generic', () => {
try {
$.throws(() => 123);
assert.unreachable('Function threw when it shouldn’t have');
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Suggested change
assert.unreachable('Function threw when it shouldn’t have');

} catch (err) {
assert.is(err.message, 'Expected function to throw');
isError(err, '', false, true, 'throws', false); // no details (true vs false)
Expand All @@ -375,6 +376,7 @@ throws('should throw if function does not throw Error :: generic', () => {
throws('should throw if function does not throw matching Error :: RegExp', () => {
try {
$.throws(() => { throw new Error('hello') }, /world/);
assert.unreachable('Function threw correct pattern when it should have thrown incorrect one');
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Suggested change
assert.unreachable('Function threw correct pattern when it should have thrown incorrect one');

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I added this in because I was confused when I changed the test to $.throws(() => { throw new Error('world') }, /world/); and it still passed. Wouldn’t the same thing happen if there was a regression in throws itself that would go unnoticed without this check?

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@aral aral Aug 11, 2021 •
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(I think this is – and the one above; same issue – are the only two I’m confused on. Accepted all other changes and happy to go with what you think is best for on these.)

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The assertion helper is saying: given X function, an error (a) should be thrown and (b) the thrown error should match {this condition}. The condition can be defined via a function, a RegExp, or a string.

So this test has X function, which happens to throw new Error('hello'), and the assertion is saying X must throw an Error that matches the /world/ pattern.

In the original test, this fails (obv because "hello" does not match /world) and so the assertions within the catch block run, and correctly find that the "Expected function to throw exception matching /world/ pattern" message appears, among others.

When you change the X to be:

$.throws(() => { throw new Error('world') }, /world/);

This doesnt fail the assertion, because "world" does match the /world pattern. The assertion passed. So in this case, the checks within the catch block never run.

Testing negated fail conditions can be a trip, haha

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I kinda feel like it could be helpful to make that work via

$.throws(() => throw new Error('world') }).matches(new Error('world'));

which maybe that doesn't make sense.. but it'd be nice to be able to chain throws() with match() rather than having a regex over err.message 🤔

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Thanks but the current API is much preferred and has prior art from many existing test runners and/or assertion libraries. It would also add a bunch of additional changes for the same (but more verbose) result.

} catch (err) {
assert.is(err.message, 'Expected function to throw exception matching `/world/` pattern');
isError(err, '', false, true, 'throws', false); // no details
Expand Down Expand Up @@ -418,6 +420,91 @@ throws.run();

// ---

const rejects = suite('rejects');

rejects('should be a function', () => {
assert.type($.rejects, 'function');
});

rejects('should throw if function does not reject Error :: generic', async () => {
try {
await $.rejects(() => {
return new Promise((resolve, reject) => {
setTimeout(() => resolve(), 1);
});
});
assert.unreachable('Promise rejected when it shouldn’t have');
} catch (err) {
assert.is(err.message, 'Expected promise to reject');
isError(err, '', false, true, 'rejects', false); // no details (true vs false)
}
});

rejects('should throw if function does not reject matching Error :: RegExp', async () => {
try {
await $.rejects(() => {
return new Promise((resolve, reject) => {
setTimeout(() => reject('hello'), 1)
});
}, /world/);
assert.unreachable('Promise rejected with correct pattern when it should have with incorrect one');
} catch (err) {
assert.is(err.message, 'Expected promise to reject matching exception `/world/` pattern');
isError(err, '', false, true, 'rejects', false); // no details
}
});

rejects('should throw if function does not reject matching Error :: Function', async () => {
try {
await $.rejects(
() => {
return new Promise((resolve, reject) => {
reject(new Error())
})
},
(err) => err.message.includes('foobar')
);
assert.unreachable('Promise should have rejected without matching exception');
} catch (err) {
assert.is(err.message, 'Expected promise to reject matching exception');
isError(err, '', false, true, 'rejects', false); // no details
}
});

rejects('should not reject if promise does reject Error :: generic', async () => {
await assert.not.rejects(
async () => await $.rejects(() => {
return new Promise ((resolve, reject) => setTimeout(() => reject(), 1));
})
, 'should not reject if function does reject Error :: generic');
});

rejects('should not reject if promise does reject matching Error :: RegExp', async () => {
await assert.not.rejects(
async () => await $.rejects(
() => {
return new Promise((resolve, reject) => setTimeout(() => reject(new Error('hello')), 1));
},
/hello/
)
);
});

rejects('should not reject if function does reject matching Error :: Function', async () => {
await assert.not.rejects(
async () => await $.rejects(
() => {
return new Promise((resolve, reject) => setTimeout(() => reject(new Error('foobar')), 1))
},
(err) => err.message.includes('foobar')
)
);
})

rejects.run();

// ---

const not = suite('not');

not('should be a function', () => {
Expand Down Expand Up @@ -793,7 +880,7 @@ notMatch.run();
const notThrows = suite('not.throws');

notThrows('should be a function', () => {
assert.type($.throws, 'function');
assert.type($.not.throws, 'function');
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});

notThrows('should not throw if function does not throw Error :: generic', () => {
Expand Down Expand Up @@ -848,3 +935,85 @@ notThrows('should throw if function does throw matching Error :: Function', () =
});

notThrows.run();

// ---

const notRejects = suite('not.throws');

notRejects('should be a function', () => {
assert.type($.not.rejects, 'function');
});

notRejects('should not reject if function does not reject Error :: generic', async () => {
await assert.not.rejects(
async () => await $.not.rejects(() => new Promise((resolve, reject) => setTimeout(() => resolve(123), 1)))
);
});

notRejects('should not reject if function does not reject matching Error :: RegExp', async () => {
await assert.not.rejects(
async () => {
await $.not.rejects(() => {
return new Promise((resolve, reject) => {
setTimeout(() => reject(new Error('hello')), 1);
})
}, /world/);
}
);
});

notRejects('should not reject if function does not reject matching Error :: Function', async () => {
await assert.not.rejects(async () => {
await $.not.rejects(() => {
return new Promise ((resolve, reject) => {
setTimeout(() => reject(new Error('hello')), 1);
})
}, (err) => err.message.includes('world'));
});
});

notRejects('should reject if function does reject Error :: generic', async () => {
try {
await $.not.rejects(() => {
return new Promise((resolve, reject) => {
setTimeout(() => reject(new Error()), 1);
});
});
assert.unreachable('Function resolved when we were expecting it to reject');
} catch (err) {
assert.is(err.message, 'Expected function not to reject promise');
isError(err, '', true, false, 'not.rejects', false); // no details
}
});

notRejects('should reject if function does reject matching Error :: RegExp', async () => {
try {
await $.not.rejects(() => {
return new Promise((resolve, reject) => {
setTimeout(() => reject(new Error('hello')), 1)
})
}, /hello/);
} catch (err) {
assert.is(err.message, 'Expected function not to reject promise exception matching `/hello/` pattern');
isError(err, '', true, false, 'not.rejects', false); // no details
}
});

notRejects('should reject if function does reject matching Error :: Function', async () => {
try {
await $.not.rejects(
() => {
return new Promise((resolve, reject) => {
setTimeout(() => reject(new Error()), 1)
})
},
(err) => err instanceof Error
);
assert.unreachable('Expected the function to reject with Error instance but it rejected with other value')
} catch (err) {
assert.is(err.message, 'Expected function not to reject promise matching exception');
isError(err, '', true, false, 'not.rejects', false); // no details
}
});

notRejects.run();