Add spec for cli generate cohort-import

These were missing, but they're useful to ensure the cli command
continues to work.

Author: misaka

spec/features/cli_generate_cohort_imports_spec.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+describe "mavis generate cohort-imports" do
+  it "generates a cohort import CSV file" do
+    given_an_organisation_exists
+    and_there_are_three_sessions_in_the_organisation
+    when_i_run_the_generate_cohort_imports_command
+    then_a_cohort_import_csv_file_is_created
+  end
+
+  def given_an_organisation_exists
+    @programme = Programme.hpv.first || create(:programme, :hpv)
+    @organisation = create(:organisation, ods_code: "R1Y")
+  end
+
+  def and_there_are_three_sessions_in_the_organisation
+    @sessions =
+      create_list(
+        :session,
+        3,
+        organisation: @organisation,
+        programmes: [@programme]
+      )
+  end
+
+  def when_i_run_the_generate_cohort_imports_command
+    freeze_time do
+      @output =
+        capture_output do
+          Dry::CLI.new(MavisCLI).call(
+            arguments: %w[generate cohort-imports -o R1Y -p 100]
+          )
+        end
+      @timestamp = Time.current.strftime("%Y%m%d%H%M%S")
+    end
+  end
+
+  def then_a_cohort_import_csv_file_is_created
+    expect(@output).to include(
+      "Generating cohort import for ods code R1Y with 100 patients"
+    )
+    expect(@output).to match(
+      /Cohort import CSV generated:.*cohort-import-R1Y-hpv-100-#{@timestamp}.csv/
+    )
+
+    expect(
+      File.readlines(
+        Rails.root.join("tmp", "cohort-import-R1Y-hpv-100-#{@timestamp}.csv")
+      ).length
+    ).to eq 101
+  end
+end