areEqualityGroups top-level constant

Matcher for == and hashCode methods of a class.

To use, invoke areEqualityGroups with a list of equality groups where each group contains objects that are supposed to be equal to each other, and objects of different groups are expected to be unequal. For example:

expect({
 'hello': ["hello", "h" + "ello"],
 'world': ["world", "wor" + "ld"],
 'three': [2, 1 + 1]
}, areEqualityGroups);

This tests that:

• comparing each object against itself returns true
• comparing each object against an instance of an incompatible class returns false
• comparing each pair of objects within the same equality group returns true
• comparing each pair of objects from different equality groups returns false
• the hash codes of any two equal objects are equal
• equals implementation is idempotent

The format of the Map passed to expect is such that the map keys are used in error messages to identify the group described by the map value.

When a test fails, the error message labels the objects involved in the failed comparison as follows:

"`[group x, item j]`" refers to the ith item in the xth equality group,
 where both equality groups and the items within equality groups are
 numbered starting from 1.  When either a constructor argument or an
 equal object is provided, that becomes group 1.