If you recall our original Hello World example, it contained a line that looked like this −
expect(message).to eq "Hello World!"
The keyword eql is an RSpec “matcher”. Here, we will introduce the other types of matchers in RSpec.
Equality/Identity Matchers
Matchers to test for object or value equality.
| Matcher | Description | Example |
|---|---|---|
| eq | Passes when actual == expected | expect(actual).to eq expected |
| eql | Passes when actual.eql?(expected) | expect(actual).to eql expected |
| be | Passes when actual.equal?(expected) | expect(actual).to be expected |
| equal | Also passes when actual.equal?(expected) | expect(actual).to equal expected |
Example
describe "An example of the equality Matchers" do
it "should show how the equality Matchers work" do
a = "test string"
b = a
# The following Expectations will all pass
expect(a).to eq "test string"
expect(a).to eql "test string"
expect(a).to be b
expect(a).to equal b
end
end
When the above code is executed, it will produce the following output. The number of seconds may be slightly different on your computer −
. Finished in 0.036 seconds (files took 0.11901 seconds to load) 1 example, 0 failures
Comparison Matchers
Matchers for comparing to values.
| Matcher | Description | Example |
|---|---|---|
| > | Passes when actual > expected | expect(actual).to be > expected |
| >= | Passes when actual >= expected | expect(actual).to be >= expected |
| < | Passes when actual < expected | expect(actual).to be < expected |
| <= | Passes when actual <= expected | expect(actual).to be <= expected |
| be_between inclusive | Passes when actual is <= min and >= max | expect(actual).to be_between(min, max).inclusive |
| be_between exclusive | Passes when actual is < min and > max | expect(actual).to be_between(min, max).exclusive |
| match | Passes when actual matches a regular expression | expect(actual).to match(/regex/) |
Example
describe "An example of the comparison Matchers" do
it "should show how the comparison Matchers work" do
a = 1
b = 2
c = 3
d = 'test string'
# The following Expectations will all pass
expect(b).to be > a
expect(a).to be >= a
expect(a).to be < b
expect(b).to be <= b
expect(c).to be_between(1,3).inclusive
expect(b).to be_between(1,3).exclusive
expect(d).to match /TEST/i
end
end
When the above code is executed, it will produce the following output. The number of seconds may be slightly different on your computer −
. Finished in 0.013 seconds (files took 0.11801 seconds to load) 1 example, 0 failures
Class/Type Matchers
Matchers for testing the type or class of objects.
| Matcher | Description | Example |
|---|---|---|
| be_instance_of | Passes when actual is an instance of the expected class. | expect(actual).to be_instance_of(Expected) |
| be_kind_of | Passes when actual is an instance of the expected class or any of its parent classes. | expect(actual).to be_kind_of(Expected) |
| respond_to | Passes when actual responds to the specified method. | expect(actual).to respond_to(expected) |
Example
describe "An example of the type/class Matchers" do
it "should show how the type/class Matchers work" do
x = 1
y = 3.14
z = 'test string'
# The following Expectations will all pass
expect(x).to be_instance_of Fixnum
expect(y).to be_kind_of Numeric
expect(z).to respond_to(:length)
end
end
When the above code is executed, it will produce the following output. The number of seconds may be slightly different on your computer −
. Finished in 0.002 seconds (files took 0.12201 seconds to load) 1 example, 0 failures
True/False/Nil Matchers
Matchers for testing whether a value is true, false or nil.
| Matcher | Description | Example |
|---|---|---|
| be true | Passes when actual == true | expect(actual).to be true |
| be false | Passes when actual == false | expect(actual).to be false |
| be_truthy | Passes when actual is not false or nil | expect(actual).to be_truthy |
| be_falsey | Passes when actual is false or nil | expect(actual).to be_falsey |
| be_nil | Passes when actual is nil | expect(actual).to be_nil |
Example
describe "An example of the true/false/nil Matchers" do
it "should show how the true/false/nil Matchers work" do
x = true
y = false
z = nil
a = "test string"
# The following Expectations will all pass
expect(x).to be true
expect(y).to be false
expect(a).to be_truthy
expect(z).to be_falsey
expect(z).to be_nil
end
end
When the above code is executed, it will produce the following output. The number of seconds may be slightly different on your computer −
. Finished in 0.003 seconds (files took 0.12301 seconds to load) 1 example, 0 failures
Error Matchers
Matchers for testing, when a block of code raises an error.
| Matcher | Description | Example |
|---|---|---|
| raise_error(ErrorClass) | Passes when the block raises an error of type ErrorClass. | expect {block}.to raise_error(ErrorClass) |
| raise_error(“error message”) | Passes when the block raise an error with the message “error message”. | expect {block}.to raise_error(“error message”) |
| raise_error(ErrorClass, “error message”) | Passes when the block raises an error of type ErrorClass with the message “error message” | expect {block}.to raise_error(ErrorClass,“error message”) |
Example
Save the following code to a file with the name error_matcher_spec.rb and run it with this command − rspec error_matcher_spec.rb.
describe "An example of the error Matchers" do
it "should show how the error Matchers work" do
# The following Expectations will all pass
expect { 1/0 }.to raise_error(ZeroDivisionError)
expect { 1/0 }.to raise_error("divided by 0")
expect { 1/0 }.to raise_error("divided by 0", ZeroDivisionError)
end
end
When the above code is executed, it will produce the following output. The number of seconds may be slightly different on your computer −
. Finished in 0.002 seconds (files took 0.12101 seconds to load) 1 example, 0 failures