ObjectMocker

The mock object library inspired by Python's mock implemented by Proxy objects.

How to install

npm install object-mocker

How to use

import {mock, getRegistry, getDeepChildHandler} from "object-mocker"; import {afterEach} from "selenium-webdriver/testing";

function getValueFromSource(source) {
    return source.loadValue();
}

const source = mock();
const result = getValueFromSource(source);

afterEach(() => {
    // clear registry after each test
    getRegistry().clear();
})

expect(result).toBe(getDeepChildHandler(source, "loadValue").report.getLastCall().returnValue);

// clear registry after test
getRegistry().clear();

Observation change the observed object!

Use only specialized functions to get nested mock objects instead of direct access by a mock object! Accessing a nested object directly create new history records and this can break test expectations.

Bad approach

import {mock, getRegistry} from "object-mocker";
const myMock = mock();

const value = myMock.child.value;

// was child accessed?
const registry = getRegistry();

expect(registry.getHandlerByObject(myMock.child).filter(r => r.type == "get" && r.property == "value").length).toBe(1)
// WRONG - GETTING THE HANDLER THIS WAY CAUSE CREATION OF NEW ACCESS RECORD! 

Good approach

import {mock, getRegistry, getDeepChildHandler} from "object-mocker";
const myMock = mock();

const value = myMock.child.value;

// was child accessed?
const registry = getRegistry();

expect(getDeepChildHandler(myMock, "child").filter(r => r.type == "get" && r.property == "value").length).toBe(1)
// OK - THERE IS ONLY ONCE RECORD

Important types

• NoEmulatedPrototype (Symbol) - declare no prototype emulation for instanceof operator.
• ResultValueFactory ((args: any[], handler: Handler) => any) - signature of factories used for making results of function calls and the new operator.
• Handler - manage actions done on mock object.
• Registry - store pairs of mock objects and their handlers.
• Report - hold information about mock object access (get property, set property, ...)

Mock objects

The mock objects are create by the mock(options?: MockOptions) function. This function has one optional argument. This argument contains configuration of the mock objects.

The MockOptions object contains only one field at this time. This field is the handlerOptions containing partial configuration of the Handler class.

Handlers

Handlers are responsible for storing usage reports and handling actions done on mock objects.

Configuration

Configuration of Handler is done by the CommonHandlerOptions interface:

• target (any?) - target object used as prototype. Default is a Function instance.
• registry (Registry) - the registry where to store child objects.
• returnValueFactory (ResultValueFactory) - factory used for return value when object is called as function.
• instanceFactory (ResultValueFactory) - factory used for create "instance" when object is used with the new operator.
• emulatedPrototype (any|NoEmulatedPrototype) - prototype used for emulation of instanceof operator.
• parent (Handler?) - handler which created this handler.
• useAutoCreate (boolean) - if true, attempt to access undefined property create new mock object and set it to this property. The undefined value is returned otherwise.

Value factories

When mock object is called as a function or used as a constructor by the new operator, return value must be generated. For this purpose there are some built in value generator factories:

• makeUniqueFactory() - make factory returning unique mock object each time called.
• makeSingletonFactory() - make factory returning new value the first time its called and then always return this value.

For custom generators see value generator signature above.

Registry

Pairs of handlers and mock objects are stored in a registry. The Registry API is:

• clear(): void - clear all records in registry.
• getObjectByHandler(handler: Handler): any - get mock object paired with given handler.
• getHandlerByObject(obj: any): Handler - get handler paired with given object.
• register(obj: any, handler: Handler): void - register a new pair of an object and a handler.
• getObjects(): any[] - get all registered objects.
• getHandlers(): any[] - get all registered handlers.

Registry related functions

• getRegistry(): Registry - get an active registry (there is always built in registry set in default).
• setRegistry(registry: Registry): void - set new active registry.

Reports

Actions, done on a mock object, are stored in reports. Following table shows observed actions and collected information:

Action	Record type
get property	PropertyGet
set property	PropertySet
delete	PropertyDelete
call as function	Call
use as construction (the new operator)	Construct

Report's methods

• getHistory() - return all usage records.
• isCalled() - return true if mock object was called at least once, false otherwise.
• getLastCall() - return last Call record or throw an Error if no call was performed.
• getCalls() - return list of all the Call records.
• getPropertyGets() - return list of all PropertyGet records.
• getPropertySets() - return list of all PropertySet records.
• getPropertyAccess(propName: string) - return all records of the property.
• filter(pred: (record: ObjectAccess) -> bool) - apply a custom filter to the history of a mock object.
• clear() - remove all records from a mock object's history.

PropertyGet

• type (str) - be always the get
• property (str) - name of the property
• value (any) - value returned by property
• wasDefined (boolean) - true if value was defined, false otherwise

PropertySet

• type (str) - be always the set
• property (str) - name of the property
• value (any) - new value of the property
• oldValue (any) - old value of the property
• created (boolean) - true if property was not defined before assignment, false otherwise

PropertyDelete

• type (str) - be always the delete
• property (str) - name of the deleted property

Call

• type (str) - be always the call
• arguments (any[]) - call arguments
• returnValue (any) - value returned by the call

Construct

• type (str) - be always the construct
• arguments (any[]) - constructor call arguments

Helper functions

• getDeepChildHandler(obj: any, path: string, autoCreate: boolean=true): Handler - get handler of the nested object. If autoCreate is true and handler is missing, the there is missing part of path, this part is created automatically. Example: const nestedHandler(myMock, "child.childOfChild")