expect

This is the top level export of the library.

The function is called with a first argument that is the "subject" of the condition we wish to checl - something that we want to make a distinct statement about:

const exampleObject = {};

jestUnexpected(exampleObject).toBeDefined();

In Unexpected parlance, the .toBeDefined() method call on the end is the assertion itself. In this case, we are stating that exampleObject must be defined in order to meet out expectations.

Errors & output

When our expectations are invaidated an error will be thrown.

let someThing;

jestUnexpected(someThing).toBeDefined();

expected undefined to be defined

Checking values

Many assertions take an additional argument that we term the "value" and allows us to specify that we our expectation is something specific, such as a string containg some specific characters or a number being positive:

const ourString = "very string";

jestUnexpected(ourString).toContain("important");

expected 'very string'

to contain ContainSpec({ spec: 'important', value: undefined, nested: false })

very string

const anInteger = 0;

jestUnexpected(anInteger).toBeGreaterThan(0);

expected 0 to be greater than 0

Assertions

We have implemented all assertions present in jest expect incuded in version 23.6.x of the library.