add stdout_check/stderr_check methods

lib/cmdtest/testcase.rb

@@ -606,8 +606,26 @@ module Cmdtest
       _stdxxx_equal_aux("stderr", false, expected)
     end
 
+    # Yield stdout to user, expecting 'assert' call.
+    def stdout_check(&block)
+      _stdxxx_check_aux("stdout", &block)
+    end
+
+    # Yield stderr to user, expecting 'assert' call.
+    def stderr_check(&block)
+      _stdxxx_check_aux("stderr", &block)
+    end
+
     # helper methods
 
+    def _stdxxx_check_aux(stdxxx)
+      _process_after do
+        @_checked[stdxxx] = true
+        str = @_effects.send(stdxxx).text(@_output_encoding, @_output_newline)
+        yield _str_as_lines(str)
+      end
+    end
+
     def _stdxxx_contain_aux(stdxxx, positive, expected)
       _process_after do
         @_checked[stdxxx] = true

t/CMDTEST_stdxxx_check.rb

@@ -0,0 +1,69 @@
+
+require "selftest_utils"
+
+class CMDTEST_stdxxx_check < Cmdtest::Testcase
+
+  include SelftestUtils
+
+  #========================================
+  # Using "define_method" to avoid duplicating definitions of
+  # stderr/stdout methods.
+
+  def self._define_stdxxx_methods(stdxxx)
+
+    #----------------------------------------
+    # stdxxx_check
+    #----------------------------------------
+
+    define_method("test_#{stdxxx}_check_CORRECT") do
+      create_CMDTEST_foo [
+        "cmd 'echo_#{stdxxx}.rb --lines A B C A' do",
+        "    #{stdxxx}_check do |lines|",
+        "        n = 0",
+        "        for line in lines",
+        "            n +=1 if line == 'A'",
+        "        end",
+        "        assert n == 2, \"A occurs \#{n} times (not 2)\"",
+        "    end",
+        "end",
+      ]
+
+      cmd_cmdtest do
+        stdout_equal [
+          "### echo_#{stdxxx}.rb --lines A B C A",
+        ]
+      end
+    end
+
+    define_method("test_#{stdxxx}_check_INCORRECT") do
+      create_CMDTEST_foo [
+        "cmd 'echo_#{stdxxx}.rb --lines A B C D' do",
+        "    #{stdxxx}_check do |lines|",
+        "        n = 0",
+        "        for line in lines",
+        "            n +=1 if line == 'A'",
+        "        end",
+        "        assert n == 2, \"A occurs \#{n} times (not 2)\"",
+        "    end",
+        "end",
+      ]
+
+      cmd_cmdtest do
+        stdout_equal [
+          "### echo_#{stdxxx}.rb --lines A B C D",
+          "--- ERROR: assertion: A occurs 1 times (not 2)",
+        ]
+        exit_nonzero
+      end
+    end
+
+  end # _define_stdxxx_methods
+
+  #----------------------------------------
+
+  for stdxxx in ["stderr", "stdout"]
+    _define_stdxxx_methods(stdxxx)
+  end
+
+end
+