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Lifecycle

Each Assert instance goes through the following steps of its lifecycle:

  • constructor
  • before
  • begin
  • assertion
  • explain
  • failure
  • report
  • finish

The constructor is passed the "actual" value by the expect static method. After the dot-chain is processed and the modifiers are accumulated, eventually an assertion method is called. When that happens, the rest of the life-cycle is run.

before

The before method is called first when the assertion method is reached. It is given the word "definition" object that defines the assertion. This is stored as _word on the Assert instance. This object is the normalized form from the registry object passed to register.

begin

This method is called passing the array of "expected" arguments (the arguments that were passed to the assertion method).

To support promises, begin checks for a pending assertion and chains its evaluation to that assertion's completion. If the "actual" value (given to the constructor) or the "expected" array have promises, begin uses Assert.Promise.all() to resolve them and calls begin again with the resolved values.

Once resolved, begin stores the array it is given as the expected property on the Assert instance.

assertion

This method is called to invoke the actual assertion logic (the evaluate method) and pass the actual and expected values. If the not modifier is present, the result is negated.

This method will set the failed property (possibly to false).

This method does nothing if called before the expected instance property is set by begin.

explain

This method is called to generate a string to explain an assertion. It is only called (by default) when an assertion fails. It is called by report before the instance is passed to the Assert.report() static method. See Integration.

In the act of generating the explanation, several other properties are set:

  • actual - A string with the printed (Assert.print) value.
  • expectation - A string with the printed (Assert.print) expected.

These are primarily of interest when writing custom assertions. See Extensibility.

failure

This method is called if the promise chain rejects and the assertion cannot be evaluated. This sets failed to the Error object given.

report

This method is called to report the Assert results. Before passing on to the Assert.report() static method (see below), this method ensures that the failed property (if set to true) has been converted to a string explaining the failure.

This method does nothing if called before the failed instance property is set by assertion.

finish

This method is called at the end of the life-cycle. It returns an object that can be used as a conjunction (via and) or a promise (via then) if the assertion was asynchronous.