Block Matchers
Block matchers observe a block of code and are used to specify a side effect that occurs when the block runs. They take the form:
| | expect { some_code }.to matcher |
As with value matchers, block matchers can be negated by using not_to or to_not rather than to.
Mutation
The change matcher captures a value before running the block (old_value) and again after running the block (new_value). The value can be specified in two ways:
| | expect { do_something }.to change(obj, :attr) |
| | # or |
| | expect { do_something }.to change { obj.attr } |
It supports a rich fluent interface for specifying further details about the mutation:
| Matcher | Passes if… |
|---|---|
change { } | old_value != new_value |
change { }.by(x) | (new_value - old_value) == x |
change { }.by_at_least(x) ... |
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