@akromio/doubles

Doubles library to simulate objects:

• Monitors to save the accesses and the calls to objects.

• Simulators to simulate the behavior of an object or a function.

You can create mocks by combining simulator and monitor.

Product of Spain, made in Valencia by Sia Codelabs.

Monitors

A monitor is an object to save the accesses to an object or the calls to a function. Similar to the spies.

Object monitor

An object monitor monitors an object: its field accesses and its method calls. We can use the monitor as the object being monitored.

We can create a monitor for an object as follows:

const {monitor} = require("@akromio/doubles");
const object = {/* ... */};

//monitor all: field accesses and calls
const m = monitor(object);

//monitor only the calls
const m = monitor(object, {onlyCalls: true});

//monitor only given members
const m = monitor(object, {members: ["member1", "member2"]});
const m = monitor(object, {members: ["method1", "method2"], onlyCalls: true});

//examples of use
console.log(m.x);       //monitored
console.log(object.x);  //not monitored, using object directly

When an object monitored, we have two kinds of entry in the log:

• Access, a member access.

• Call, a function object call.

When a method is accessed, we can't forget that two operations are performed:

1. The access to the function object.

2. The function object call.

If only the method calls must be monitored, use the onlyCalls option.

Function monitor

A function monitor monitors a function. We can use the monitor as the function object being monitored.

We can create a monitor for a function object as follows:

const {monitor} = require("@akromio/doubles");
function fn(/*...*/) { /* ... */ }

//monitor function calls
const m = monitor(fn);

//examples of use
console.log(m(1, 2));   //monitored
console.log(fn(1, 2));  //not monitored, using function object directly

Monitor clear

To clear a monitor:

const m = monitor({});
monitor.clear(m);

Monitor log

A monitor has a log, where the accesses and the calls are saved. To get the log associated to a monitor, use the monitor.log() function:

function log(m, opts?: {clear: boolean}): any

If clear specified, monitor.clear(m) is performed too.

Example:

const m = monitor({});

//work with m

const log = monitor.log(m);

Operations with the log

//number of calls, not keeping in mind the field accesses
log.calls

//number of field accesses, not keeping in mind the calls
log.accesses

//number of log entries (calls + accesses)
log.len

//number of operations returning
log.returns

//number of times a given value returned
log.returnedValue(value)

//number of times a value returned of a given type
log.returnedType(Type)

//number of operations raising an error
log.raises

//number of times a given value raised
log.raisedValue(value)

//number of times a value raised of a given type
log.raisedType(Type)

//number of times called with a given arguments
log.calledWith([arg1, arg2...])

//given entry by its index in the log
log.getEntry(i)

//given call by its index in the log, not keeping in mind the accesses
log.getCall(i)

//given field access by its index in the log, not keeping in mind the calls
log.getAccess(i)

When getEntry(), getCall() or getAccess() used, the instances returned are of the following types:

• Access, representing a field access:

  Member | Date type | Description -- | -- | -- member | string | Member name. value | any | Value returned or raised. returned | boolean | Did the access return a value? raised | boolean | Did the access raise an error? returnedValue(value) | boolean | Was the given value returned? returnedType(Type) | boolean | Is the returned value of the given type? raisedValue(value) | boolean | Was the given value raised? raisedType(Type) | boolean | Is the raised value of the given type? isGet() | boolean | Is a read access? isSet() | boolean | Is a write access?

• Call, representing a function/method call:

  Member | Date type | Description -- | -- | -- value | any | Value returned or raised by the call. returned | boolean | Did the call return a value? raised | boolean | Did the call raise an error? returnedValue(value) | boolean | Was the given value returned? returnedType(Type) | boolean | Is the returned value of the given type? raisedValue(value) | boolean | Was the given value raised? raisedType(Type) | boolean | Is the raised value of the given type? calledWith([arg1, arg2...]) | boolean | Were the given arguments passed to the call?

Examples:

const log = monitor.log(m);

expected(log.calls).equalTo(1);
expected(log.getCall(0)).toHave({value: 123});

Simulator

A simulator is an object to simulate another, defining only the responses.

Function simulator

A function simulator is a simulator for a function. This is defined with the simulator.fun() function:

//returning always null
simulator.fun(): function

//returning attending to given behavior/responses
simulator.fun(behavior: object[]|object): function

The behavior is an object containing the responses for the calls. If we always want to perform the same operation, we can use an object, as follows:

fn = simulator.fun({returns: 1234});
fn(/*...*/)  //returns 1234

fn = simulator.fun({raises: new Error("my error")});
fn(/*...*/)  //throws the error

fn = simulator.fun({resolves: 1234});
await(fn(/*...*/))  //returns 1234

fn = simulator.fun({rejects: new Error("my error")});
await(fn(/*...*/))  //throws the error

The following fields are possible:

Field | Data type | Description -- | -- | -- returns | any | Value to return. raises | any | Value to raise. resolves | any | Value to return using a resolved promise. rejects | any | Value to raise using a rejected promise. invokes | function | Function to call, the value returned by this function will be the value returned. The arguments passed to the simulated function are passed to the function.

But if we want to select among several possibilities, we have to use an array of objects. Two types are possible: position-based or arguments-based.

On the one hand, we can use a position-based behavior, keeping in mind the arguments passed to the calls aren't used. In this case, the first response must contain the i field set to 0. Example:

const m = simulator.fun([
  {i: 0, returns: 1234},
  {returns: 5678},
  {default: true, returns: 13579}
]);

m("one")    //returns 1234
m("two")    //returns 5678
m("three")  //returns 13579
m("four")   //returns 13579

The default response, defined with default to true, is used when call out of range. If not defined, in the previous example, the third and fourth calls will raise an error.

On the other hand, we have the arguments-based behavior, using the arguments to select the response. These are defined with an args field. Example:

fn = simulator.fun([
  {default: true, returns: "default value"},
  {args: [12, 34], returns: 1234},
  {args: [34, 12], raises: new Error("my error")},
  {args: [12, 34, 56], resolves: 135},
  {args: [56, 34, 12], rejects: new Error("my error")}
]);

fn()                  //returns "default value", arguments not found in the responses
fn(34, 12)            //throws error
fn(12, 34)            //returns 1234
await(fn(56, 34, 12)) //throws error
await(fn(12, 34, 56)) //returns 135
fn(1, 3, 5, 7, 9)     //returns "default value", arguments not found in the responses

If the function simulator must simulate fields too, we can define its members in the second argument of simulator.fun():

fn = simulator.fun(
  {returns: 1234},  //always returns  1234, but this argument can be an array
  {
    x: simulator.field({returns: "value of x"}),
    y: simulator.field({returns: "value of y"})
  }
);

fn()        //returns 1234
fn(12, 34)  //returns 1234
fn.x        //returns value of x
fn.y        //returns value of y

Object simulator

An object simulator is a simulator for a (non-callable) object. These are created with simulator():

const {simulator} = require("@akromio/doubles");
const {field, fun} = simulator;

const obj = simulator({
  member1: field(/*...*/),
  member2: fun(/*...*/)
});

The fields must be defined with simulator.field() and the methods with simulator.fun() or its alias simulator.method().

Example:

const {simulator} = require("@akromio/doubles");
const {field, fun} = simulator;

const m = simulator({
  x: field({returns: 12}),
  y: field({raises: new Error("my error")}),
  z: fun({returns: 1234})
});

m.x   //returns 12
m.y   //raises an error
m.z() //returns 1234

The fields can have position-based behaviors if needed, defined as seen with simulator.fun().

Special fields

simulator.field.uuid()         //similar to: simulator.field({default: true, returns: uuid.v4()})
simulator.field.list(returns)  //similar to: simulator.field({default: true, returns: returns ?? []})
simulator.field.map(returns)   //similar to: simulator.field({default: true, returns: returns ?? {}})
simulator.field.text(returns)  //similar to: simulator.field({default: true, returns: "text to return"})
simulator.field.bool(returns)  //similar to: simulator.field({default: true, returns: true|false})
simulator.field.any(returns)   //similar to: simulator.field({default: true, returns: value})

Important. When a returns passed, a clone of the value is used. So well, the original value is not modified.