diff --git a/lib/cmdtest/testcase.rb b/lib/cmdtest/testcase.rb
index 553d43b..5bf38bf 100644
--- a/lib/cmdtest/testcase.rb
+++ b/lib/cmdtest/testcase.rb
@@ -63,7 +63,7 @@ module Cmdtest
 
     ORIG_CWD = Dir.pwd
 
-    attr_reader :_work_dir, :_cwd
+    attr_reader :_work_dir, :_cwd, :_env
 
     def initialize(test_method, clog, runner)
       @_test_method = test_method
@@ -71,6 +71,7 @@ module Cmdtest
       @_runner = runner
       @_work_dir = Workdir.new(self, runner)
       @_cwd = self.tmp_work_dir
+      @_env = Hash.new
       @_in_cmd = false
       @_comment_str = nil
       @_env_path = @_runner.orig_env_path
@@ -184,6 +185,18 @@ module Cmdtest
 
     #------------------------------
 
+    def setenv(name, value)
+      @_env[name] = value
+    end
+
+    #------------------------------
+
+    def unsetenv(name)
+      @_env.delete(name)
+    end
+
+    #------------------------------
+
     def current_directory
       @_cwd
     end
diff --git a/lib/cmdtest/workdir.rb b/lib/cmdtest/workdir.rb
index 809f386..52721f5 100644
--- a/lib/cmdtest/workdir.rb
+++ b/lib/cmdtest/workdir.rb
@@ -75,6 +75,10 @@ module Cmdtest
       File.join(@testcase.tmp_dir, "tmp-stderr.log")
     end
 
+    def _ENV_strs(env)
+      env.keys.sort.map {|k| "export %s='%s'" % [k, env[k]] }
+    end
+
     def _chdir_str(dir)
       "cd #{dir}"
     end
@@ -101,6 +105,7 @@ module Cmdtest
 
     def run_cmd(cmdline, env_path)
       File.open(_tmp_command_sh, "w") do |f|
+        f.puts _ENV_strs(@testcase._env)
         f.puts _chdir_str(@testcase._cwd)
         f.puts _set_env_path_str(env_path)
         f.puts _ruby_S(cmdline)