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start_with matcher

Use the start_with matcher to specify that a string or array starts with the expected characters or elements.

expect("this string").to start_with("this")
expect("this string").not_to start_with("that")
expect([0,1,2]).to start_with(0, 1)

With a string​

Given a file named "example_spec.rb" with:

RSpec.describe "this string" do
  it { is_expected.to start_with "this" }
  it { is_expected.not_to start_with "that" }

  # deliberate failures
  it { is_expected.not_to start_with "this" }
  it { is_expected.to start_with "that" }
end

When I run rspec example_spec.rb

Then the output should contain all of these:

| 4 examples, 2 failures | | expected "this string" not to start with "this" | | expected "this string" to start with "that" |

With an array​

Given a file named "example_spec.rb" with:

RSpec.describe [0, 1, 2, 3, 4] do
  it { is_expected.to start_with 0 }
  it { is_expected.to start_with(0, 1)}
  it { is_expected.not_to start_with(2) }
  it { is_expected.not_to start_with(0, 1, 2, 3, 4, 5) }

  # deliberate failures
  it { is_expected.not_to start_with 0 }
  it { is_expected.to start_with 3 }
end

When I run rspec example_spec.rb

Then the output should contain all of these:

| 6 examples, 2 failures | | expected [0, 1, 2, 3, 4] not to start with 0 | | expected [0, 1, 2, 3, 4] to start with 3 |