testing/asserts : `assertFalse`

[UltiRequiem]

Is your feature request related to a problem? Please describe.

Currently, the testing module lacks a method to check if a value is False.

Describe the solution you'd like

export function assertFalse(expr: unknown, msg = ""): asserts expr is false {
  if (expr) {
    throw new AssertionError(msg);
  }
}

Describe alternatives you've considered

Deno.test("Text with letter is not numeric.", () => {
  assertEquals(isNumber("hello"), false);
  assert(isNumber("hello") === false);
  assert(!isNumber("hello"));
});

With the solution shown before we could

Deno.test("Text with letter is not numeric.", () => {
  assertFalse(isNumber("hello"));
});

Which I think is a lot more readable. Similar to 👇🏽 https://jestjs.io/docs/expect#tobefalsy https://github.com/avajs/ava/blob/main/docs/03-assertions.md#falseactual-message

[getspooky]

@UltiRequiem you can use assert or assertEquals so no need to add assertFalse

[UltiRequiem]

@UltiRequiem you can use assert or assertEquals so no need to add assertFalse

I already listed both options on Describe alternatives you've considered.

Despite that, an assertFalse function would upgrade readability and other libraries include it.

[UltiRequiem]

Another library that has something similar is Ava.

https://github.com/avajs/ava/blob/main/docs/03-assertions.md#falseactual-message

[kt3k]

This looks too trivial to include in std to me.

Is there any supportive opinions to this other than the above?

[UltiRequiem]

This looks too trivial to include in std to me.

Is there any supportive opinions to this other than the above?

I think the two strongest points are readability, and that other frameworks have it.

But I understand if it is not wanted here 😆

[bcheidemann]

I don't have a strong opinion if this should be implemented or not.

However, it should be assertNot in my opinion to match the existing convention set by other assertions e.g. assertEquals() vs assertNotEquals().

[bcheidemann]

@bartlomieju @kt3k can we make a call yet on if we want to include this or not? The reasons for including it seem valid to me and I know I (and many other developers) would use it even though it is trivial 😉

[bartlomieju]

If there's prior art for such assertion I'm willing to squint my eyes and accept it.

[kt3k]

Researched other languages and libraries. Some languages seem intentionally avoiding including it (Node, Ruby, Rust, etc), but many languages/libraries seem having assertFalse or similar. Interestingly I couldn't find any example of assertNot, which I personally think is worth considering.

Libs/Languages which have something similar to assertFalse

• JUnit (Java) has assertTrue and assertFalse https://junit.org/junit5/docs/5.0.1/api/org/junit/jupiter/api/Assertions.html#assertFalse-boolean-
• QUnit (JUnit clone in javascript) has assert.true and assert.false https://api.qunitjs.com/assert/false/
• Kotlin has assert and assertFalse https://kotlinlang.org/api/latest/kotlin.test/kotlin.test/assert-false.html
• Python unittest has assertTrue and assertFalse https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertFalse
• Golang testify has assert.True and assert.False https://pkg.go.dev/github.com/stretchr/testify/assert#False
• PHPUnit has assertTrue and assertFalse https://phpunit.readthedocs.io/en/9.5/assertions.html

Libs/Languages which don't have something similar to assertFalse

• Node.js has assert() and doesn't have negative version https://nodejs.org/api/assert.html
• Ruby has assert and doesn't have negative version https://docs.ruby-lang.org/en/2.1.0/Test/Unit/Assertions.html
• Rust has assert! and doesn't have negative version https://doc.rust-lang.org/std/macro.assert.html
• OCaml's OUnit has assert_bool (similar to assert_true) and doesn't have negative version https://gildor478.github.io/ounit/ounit2/OUnit2/index.html#val-assert_bool

[bcheidemann]

@kt3k That's very interesting 🤔 seems like a fairly even split.

I think assertFalse makes sense for many of the other languages mentioned because they have much narrower definitions of what it means to be falsy.

In JS I think it is misleading because assertFalse(""); assertFalse(0); assertFalse(null); assertFalse(undefined); assertFalse(NaN); would all pass.

I suggested assertNot because it fits the pattern for inverse assertions in deno_std but I think assertFalsy would also make sense. This would match Jest which has expect.toBeFalsy.

I think Jest also has toBeTrue and toBeFalse but these match only the literal values true and false.

[bartlomieju]

@kt3k since there are more examples of support for this feature I think we can add it.

[UltiRequiem]

Closing because the feature was merged.