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Fundamentals of Testing Using Rails

RSpec Predefined Matchers

Get an overview of RSpec's basic and predefined matchers.

We'll cover the following...

Built-in RSpec matchers

Before we run the tests, let’s take a quick look at RSpec’s basic matchers. RSpec predefines several matchers. What follows is a list of the most useful ones. We can find them in their official documentation as well.

Some examples are:

Ruby
expect(array).to all(matcher)
expect(actual).to be > expected # (also works with <, >=, <=, and ==)
expect(actual).to be_a(type)
expect(actual).to be_truthy
expect(actual).to be_falsy
expect(actual).to be_nil
expect(actual).to be_between(min, max)
expect(actual).to be_within(delta).of(expected)
expect { block }.to change(receiver, message, &block)
expect(actual).to contain_exactly(expected)
expect(range).to cover(actual_value)
expect(actual).to eq(expected)
expect(actual).to exist
expect(actual).to have_attributes(key/value pairs)
expect(actual).to include(*expected)
expect(actual).to match(regex)
expect { block }.to output(value).to_stdout # also to_stderr
expect { block }.to raise_error(exception)
expect(actual).to satisfy { block }

Most of these mean what they appear to say. A few are ...