org.scalatest.junit.JUnitSuite

Equalizer

class Equalizer extends AnyRef

Class used via an implicit conversion to enable any two objects to be compared with === in assertions in tests. For example:

assert(a === b)

The benefit of using assert(a === b) rather than assert(a == b) is that a TestFailedException produced by the former will include the values of a and b in its detail message. The implicit method that performs the conversion from Any to Equalizer is convertToEqualizer in trait Assertions.

In case you're not familiar with how implicit conversions work in Scala, here's a quick explanation. The convertToEqualizer method in Assertions is defined as an "implicit" method that takes an Any, which means you can pass in any object, and it will convert it to an Equalizer. The Equalizer has === defined. Most objects don't have === defined as a method on them. Take two Strings, for example:

assert("hello" === "world")

Given this code, the Scala compiler looks for an === method on class String, because that's the class of "hello". String doesn't define ===, so the compiler looks for an implicit conversion from String to something that does have an === method, and it finds the convertToEqualizer method. It then rewrites the code to this:

assert(convertToEqualizer("hello").===("world"))

So inside a Suite (which mixes in Assertions, === will work on anything. The only situation in which the implicit conversion wouldn't happen is on types that have an === method already defined.

The primary constructor takes one object, left, whose type is being converted to Equalizer. The left value may be a null reference, because this is allowed by Scala's == operator.

attributes: final
definition classes: Assertions

Inherits

  1. AnyRef
  2. Any

Value Members

  1. def ===(right: Any): Option[String]

    The === operation compares this Equalizer's left value (passed to the constructor, usually via an implicit conversion) with the passed right value for equality as determined by the expression left == right

    The === operation compares this Equalizer's left value (passed to the constructor, usually via an implicit conversion) with the passed right value for equality as determined by the expression left == right. If true, === returns None. Else, === returns a Some whose String value indicates the left and right values.

    In its typical usage, the Option[String] returned by === will be passed to one of two of trait Assertion' overloaded assert methods. If None, which indicates the assertion succeeded, assert will return normally. But if Some is passed, which indicates the assertion failed, assert will throw a TestFailedException whose detail message will include the String contained inside the Some, which in turn includes the left and right values. This TestFailedException is typically embedded in a Report and passed to a Reporter, which can present the left and right values to the user.

  2. def equals(arg0: Any): Boolean

    This method is used to compare the receiver object (this) with the argument object (arg0) for equivalence

    This method is used to compare the receiver object (this) with the argument object (arg0) for equivalence.

    The default implementations of this method is an equivalence relation:

    • It is reflexive: for any instance x of type Any, x.equals(x) should return true.
    • It is symmetric: for any instances x and y of type Any, x.equals(y) should return true if and only if y.equals(x) returns true.
    • It is transitive: for any instances x, y, and z of type AnyRef if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.

    If you override this method, you should verify that your implementation remains an equivalence relation. Additionally, when overriding this method it is often necessary to override hashCode to ensure that objects that are "equal" (o1.equals(o2) returns true) hash to the same Int (o1.hashCode.equals(o2.hashCode)).

    arg0

    the object to compare against this object for equality.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    definition classes: AnyRef ⇐ Any
  3. def hashCode(): Int

    Returns a hash code value for the object

    Returns a hash code value for the object.

    The default hashing algorithm is platform dependent.

    Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)) yet not be equal (o1.equals(o2) returns false). A degenerate implementation could always return 0. However, it is required that if two objects are equal (o1.equals(o2) returns true) that they have identical hash codes (o1.hashCode.equals(o2.hashCode)). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the equals method.

    definition classes: AnyRef ⇐ Any
  4. def toString(): String

    Returns a string representation of the object

    Returns a string representation of the object.

    The default representation is platform dependent.

    definition classes: AnyRef ⇐ Any

Instance constructors

  1. new Equalizer(left: Any)

  2. new Equalizer()