fix: the error output is incorrect

Author: LinuxSuRen

command.go

@@ -102,7 +102,8 @@ func (e DefaultExecer) RunCommandAndReturn(name, dir string, args ...string) (re
 	if err = e.RunCommandWithBuffer(name, dir, stdout, stderr, args...); err == nil {
 		result = stdout.String()
 	} else {
-		result = stderr.String()
+		result = stdout.String()
+		result += stderr.String()
 	}
 	return
 }

fake-command.go

@@ -40,7 +40,8 @@ func (f FakeExecer) RunCommandAndReturn(name, dir string, args ...string) (resul
 	if err = f.ExpectError; err == nil {
 		result = f.ExpectOutput
 	} else {
-		result = f.ExpectErrOutput
+		result = f.ExpectOutput
+		result += f.ExpectErrOutput
 	}
 	return
 }

fake-command_test.go

@@ -42,9 +42,10 @@ func TestLookPath(t *testing.T) {
 
 	fakeWithErr := FakeExecer{
 		ExpectError:     errors.New("fake"),
+		ExpectOutput:    "output",
 		ExpectErrOutput: "error",
 	}
 	result, err = fakeWithErr.RunCommandAndReturn("", "")
-	assert.Equal(t, "error", result)
+	assert.Equal(t, "outputerror", result)
 	assert.NotNil(t, err)
 }