# jest-mock

## API

### `constructor(global)`

Creates a new module mocker that generates mocks as if they were created in an
environment with the given global object.

### `generateFromMetadata(metadata)`

Generates a mock based on the given metadata (Metadata for the mock in
the schema returned by the getMetadata method of this module). Mocks treat
functions specially, and all mock functions have additional members, described
in the documentation for `fn` in this module.


One important note: function prototypes are handled specially by this
mocking framework. For functions with prototypes, when called as a
constructor, the mock will install mocked function members on the instance.
This allows different instances of the same constructor to have different
values for its mocks member and its return values.

### `getMetadata(component)`

Inspects the argument and returns its schema in the following recursive format:

```js
{
  type: ...
  members : {}
}
```

Where type is one of `array`, `object`, `function`, or `ref`, and members
is an optional dictionary where the keys are member names and the values
are metadata objects. Function prototypes are defined simply by defining
metadata for the `member.prototype` of the function. The type of a function
prototype should always be `object`. For instance, a simple class might be
defined like this:

```js
{
  type: 'function',
  members: {
    staticMethod: {type: 'function'},
    prototype: {
      type: 'object',
      members: {
        instanceMethod: {type: 'function'}
      }
    }
  }
}
 ```

Metadata may also contain references to other objects defined within the
same metadata object. The metadata for the referent must be marked with
`refID` key and an arbitrary value. The referrer must be marked with a
`ref` key that has the same value as object with refID that it refers to.
For instance, this metadata blob:

```js
{
  type: 'object',
  refID: 1,
  members: {
    self: {ref: 1}
  }
}
```

defines an object with a slot named `self` that refers back to the object.

### `fn`

Generates a stand-alone function with members that help drive unit tests or
confirm expectations. Specifically, functions returned by this method have
the following members:

##### `.mock`

An object with two members, `calls`, and `instances`, which are both
lists. The items in the `calls` list are the arguments with which the
function was called. The "instances" list stores the value of 'this' for
each call to the function. This is useful for retrieving instances from a
constructor.

##### `.mockReturnValueOnce(value)`

Pushes the given value onto a FIFO queue of return values for the
function.

##### `.mockReturnValue(value)`

Sets the default return value for the function.

##### `.mockImplementationOnce(function)`

Pushes the given mock implementation onto a FIFO queue of mock
implementations for the function.

##### `.mockImplementation(function)`

Sets the default mock implementation for the function.

##### `.mockReturnThis()`

Syntactic sugar for .mockImplementation(function() {return this;})



In case both `mockImplementationOnce()/mockImplementation()` and
`mockReturnValueOnce()/mockReturnValue()` are called. The priority of which to
use is based on what is the last call:
- if the last call is mockReturnValueOnce() or mockReturnValue(),
  use the specific return value or default return value.
  If specific return values are used up or no default return value is set,
  fall back to try mockImplementation();
- if the last call is mockImplementationOnce() or mockImplementation(),
  run the specific implementation and return the result or run default
  implementation and return the result.