Kata

The test doesn't match the description.

echo "9 30 28 1 3 12 8 4 16 29" # valid
# it's also valid even if the solution prints 1..31

Also, the delimiter is not specified. Most solutions assumes \n.

Keeping it very basic to try out test cases.

The following can be used to test if the output is exactly 1..30.

describe "Loop" do
  it "Tests" do
    expect(run_shell.split("\n").map {|x| x.to_i}).to eq((1..30).to_a)
  end
end

You can also do random tests if you're willing to change the kata to print to arbitrary maximum.

it "Random" do
  10.times { # Print numbers 1..n
    n = rand(1..30)
    expect((run_shell args: [n]).split("\n").map {|x| x.to_i}).to eq((1..n).to_a)
  }
end