Why do we need tests?.… Automated testing means that tests are written separately, in addition to the code.… Tests start to fail.
Go to 3, update the implementation till tests give no errors.… function that runs tests.… (or test groups).
For instance, let’s test if the text starts with Mary:… Similar to this, we can test if the string ends with snow using snow$:… Regular expressions should be used for more complex tests.… Testing for a full match.Both anchors together ^...$ are often used to test whether or not a string fully… Anchors have “zero width”
Anchors ^ and $ are tests. They have zero width.
A word boundary \b is a test, just like ^ and $.… So, it matches the pattern \bHello\b, because:
At the beginning of the string matches the first test… Then the test \b matches again, as we’re between o and a comma.… Word boundary \b doesn’t work for non-latin alphabets
The word boundary test \b checks that… But \w means a latin letter a-z (or a digit or an underscore), so the test doesn’t work for other characters
Please note:
“Start of a line” formally means “immediately after a line break”: the test… Please note:
“End of a line” formally means “immediately before a line break”: the test… Unlike the anchors ^ $, that only test the condition (start/end of a line), \n is a character, so it
Please note: the lookahead is merely a test… More complex tests are possible, e.g. X(?=Y)(?=Z) means:
Find X.… If both tests passed, then the X is a match, otherwise continue searching.… =€) is just a test that it should be followed by €.
gets “input” variables and produces certain “outcome” is clearer, less prone to errors and easier to test… Using for polyfills.We use the global object to test for support of modern language features.… For instance, test if a built-in Promise object exists (it doesn’t in really old browsers):
Tests: isFinite and isNaN.Remember these two special numeric values?… are special functions to check for them:
isNaN(value) converts its argument to a number and then tests… For regular number tests:
isNaN(value) converts its argument to a number and then tests it for being… NaN
Number.isNaN(value) checks whether its argument belongs to the number type, and if so, tests it… Infinity
Number.isFinite(value) checks whether its argument belongs to the number type, and if so, tests
As var ignores code blocks, we’ve got a global variable test… If we used let test instead of var test, then the variable would only be visible inside if:
Several conditions: “else if”.Sometimes, we’d like to test… But after a closer look, we can see that it’s just an ordinary sequence of tests:
The first question
Property existence test, “in” operator.A notable feature of objects in JavaScript, compared to many other… So we can easily test whether the property exists:… If we omit quotes, that means a variable should contain the actual name to be tested.
whole project (not just the open file), and integrates with a version management system (like git), a testing
That may be helpful for automated testing.… For automated testing, to “click the button” in the script and see if the interface reacts correctly.
Same global regexp tested… That’s exactly because regexp.lastIndex is non-zero in the second test
It happens in logical operations (later we’ll meet condition tests and other similar things) but can
So the test of obj instanceof Class can be rephrased as Class.prototype.isPrototypeOf(obj).
If we check event.code == 'KeyZ' in our code, then for people with German layout such test will pass… prevents the default action, so nothing appears in the <input> for keys that don’t pass the test
A separate function is not only easier to test and debug – its very existence is a great comment!… The second variant uses an additional function isPrime(n) to test
Constructor mode test: new.target.
There is a slight inconvenience with indexOf in the if test.… It’s the right choice if we need to test for the match, but don’t need its position:
And also there are tests for them:
Object.isExtensible(obj)
Returns false if adding properties is forbidden
Most of the time, OR || is used in an if statement to test
For instance, this function returns a resolved promise with the result of 1; let’s test it:
Proxies can’t intercept a strict equality test ===
Proxies can intercept many operators,… But there’s no way to intercept a strict equality test for objects.… Object equality tests === can’t be intercepted.
Equals: a == b, please note the double equality sign == means the equality test, while a single one a
You might want to open this page in two browser windows to test the code below.
How Map compares keys
To test keys for equivalence, Map uses the algorithm SameValueZero.
That’s to guarantee that there’s no side way for an evil page to test if a link was visited and hence
Here’s a more flexible test… Here’s the test stand to see them in action:
That is, begin executes once, and then it iterates: after each condition test
They may tweak results of “artificial tests” compared to “normal usage”, especially when we benchmark
points:
Because of that last property, in computer graphics it’s possible to optimize intersection tests
If your browser reserves the space for a scrollbar (most browsers for Windows do), then you can test
If you run the code below, it replaces the opener (current) window content with “Test”:
Some regular expression engines have tricky tests and finite automations that allow to avoid going through
static-server or use the “live server” capability of your editor, such as VS Code Live Server Extension to test
practical uses, for instance, as a random number generator to generate random values for automated tests
In modern scripts, we can use instanceof and other class-based tests