Rails 7.1 makes it possible to execute tests for a given range of lines in a file

railsSeptember 06, 2023by Alkesh Ghorpade

In Rails 7.1, developers can now run tests for a specific section of code by passing a line range (a-b) to the rails test command.

Before Rails 7.1

Consider a large test file with 100 tests, and you want to run the tests from line 20 to line 30.

class MathTest < ActiveSupport::TestCase
  test "sum" do
  end
  ....
  ....
  test "square_root" do # line 20
  end
  ....
  ....
  test "if_number_is_a_perfect_square" do # line 25
  end
  ....
  ....
  test "if_number_is_prime" do # line 30
  end
  ....
  ....
  .... # the rest of the lines
end

Before Rails 7.1, if you wanted to run the tests from lines 20 to 30, you had to execute them individually by specifying the line number or passing the method name.

rails test test/math_test.rb:20
rails test test/math_test.rb:25
rails test test/math_test.rb:30

# passing the method name

rails test test/math_test.rb -n test_square_root
rails test test/math_test.rb -n test_if_number_is_a_perfect_square
rails test test/math_test.rb -n test_if_number_is_prime

Specifying the line number or method name is useful for running a single test case, but it is not ideal for running multiple tests within a given line range.

In Rails 7.1

Rails 7.1 allows running tests for a given line range in a file.

To execute tests in a given line range, you can use the following command:

rails test test/math_test.rb:20-30

Running 5 tests in a single process (parallelization threshold is 50)
Run options: --seed 11201

# Running:

.....

Finished in 0.010102s, 143.2322 runs/s, 143.2322 assertions/s.
5 runs, 5 assertions, 0 failures, 0 errors, 0 skips

To execute specs between two line ranges, 20-30 and 50-75, you need to execute the below command:

rails test test/math_test.rb:20-30:50-75

A combination of line range and a single test can be executed by passing the line range followed by the single test line number.

rails test test/math_test.rb:20-30:50

Note:

The test command range will fail with LoadError for the following line range.

Negative line range

rails test test/math_test.rb:-20-30

`require': cannot load such file -- /rails/tmp/d20230906-53282-66wxlt/app/test/math_test.rb:-20-30 (LoadError)

Not passing the line range

rails test test/math_test.rb:-30

`require': cannot load such file -- /rails/tmp/d20230906-53282-66wxlt/app/test/math_test.rb:-30 (LoadError)


rails test test/math_test.rb:20-

`require': cannot load such file -- /rails/tmp/d20230906-53282-66wxlt/app/test/math_test.rb:20- (LoadError)

To know more about this feature, please refer to this PR.

Closing Remark

Could your team use some help with topics like this and others covered by ShakaCode's blog and open source? We specialize in optimizing Rails applications, especially those with advanced JavaScript frontends, like React. We can also help you optimize your CI processes with lower costs and faster, more reliable tests. Scraping web data and lowering infrastructure costs are two other areas of specialization. Feel free to reach out to ShakaCode's CEO, Justin Gordon, at justin@shakacode.com or schedule an appointment to discuss how ShakaCode can help your project!

Alkesh Ghorpade

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