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
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