require file argument to 'import_file' + test

lib/cmdtest/testcase.rb

@@ -26,6 +26,7 @@ require "stringio"
 module Cmdtest
 
   class AssertFailed < RuntimeError ; end
+  class UsageError < RuntimeError ; end
 
   # Base class for testcases.
   # Some attributes and methods are prefixed with an "_" to avoid
@@ -88,7 +89,11 @@ module Cmdtest
       src_path = File.expand_path(src, @_runner.test_files_top)
       tgt_path = _cwd_path(tgt)
       FileUtils.mkdir_p(File.dirname(tgt_path))
-      FileUtils.cp(src_path, tgt_path)
+      if File.file?(src_path)
+        FileUtils.cp(src_path, tgt_path)
+      else
+        raise UsageError, "'import_file' argument not a file: '#{src}'"
+      end
     end
 
     #------------------------------

t/CMDTEST_import_file.rb

@@ -9,6 +9,22 @@ class CMDTEST_import_file < Cmdtest::Testcase
   # import_file
   #----------------------------------------
 
+  def test_import_file_ERROR
+    create_file "file1.dir/empty.txt", ""
+
+    create_CMDTEST_foo [
+      "import_file 'file1.dir', 'qwerty1.dir'",
+    ]
+
+    cmd_cmdtest do
+      stdout_equal /CAUGHT EXCEPTION:/
+      stdout_equal /'import_file' argument not a file: 'file1.dir'/
+      exit_nonzero
+    end
+  end
+
+  #----------------------------------------
+
   def test_import_file_DIFFERENT_DIRS
     create_file "file1.txt", "This is file1.txt\n"
     create_file "file2.txt", "This is file2.txt\n"