I'm using Jest to test my Node application.
Is it possible for me to expect/assert a value to be a Date Object?
expect(typeof result).toEqual(typeof Date())
Was my attempt, but naturally returns [Object]. And so this would pass too {}.
Thanks!
3 Answers
for Jest with newer version > 16.0.0:
There is a new matcher called toBeInstanceOf. You can use the matcher to compare instances of a value.
Example:
expect(result).toBeInstanceOf(Date)
for Jest with version < 16.0.0:
Use instanceof to prove whether the result variable is a Date Object or Not.
Example:
expect(result instanceof Date).toBe(true)
Another example to match common types:
boolean
expect(typeof target).toBe("boolean")
number
expect(typeof target).toBe("number")
string
expect(typeof target).toBe("string")
array
expect(Array.isArray(target)).toBe(true)
object
expect(target && typeof target === 'object').toBe(true)
null
expect(target === null).toBe(true)
undefined
expect(target === undefined).toBe(true)
function
expect(typeof target).toBe('function')
Promise or async function
expect(!!target && typeof target.then === 'function').toBe(true)
Another example to match further types:
float (decimal number. i.e. 3.14, 137.03, etc.)
expect(Number(target) === target && target % 1 !== 0).toBe(true)
Promise or async function that return an Error
await expect(asyncFunction()).rejects.toThrow(errorMessage)
References:
Jest supports toBeInstanceOf. See their docs, but here is what they have for example at the time of this answer:
class A {}
expect(new A()).toBeInstanceOf(A);
expect(() => {}).toBeInstanceOf(Function);
expect(new A()).toBeInstanceOf(Function); // throws
if you are dealing with JSX you can do the following
expect(result.type).toBe(MyComponent);
Example:
component = shallow(<MyWidget {...prop} />);
instance = component.instance();
const result = instance.myMethod();
expect(result.type).toBe(MyComponent);
In this example myMethod() return MyComponent and we are testing for it.
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