Add test that demonstrates bug with language auto-detection

pkg/i18n/i18n_test.go

@@ -2,8 +2,11 @@ package i18n
 
 import (
 	"fmt"
+	"io"
+	"runtime"
 	"testing"
 
+	"github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -33,3 +36,84 @@ func TestDetectLanguage(t *testing.T) {
 		assert.EqualValues(t, s.expected, detectLanguage(s.langDetector))
 	}
 }
+
+// Can't use utils.NewDummyLog() because of a cyclic dependency
+func newDummyLog() *logrus.Entry {
+	log := logrus.New()
+	log.Out = io.Discard
+	return log.WithField("test", "test")
+}
+
+func TestNewTranslationSetFromConfig(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		// These tests are based on setting the LANG environment variable, which
+		// isn't respected on Windows.
+		t.Skip("Skipping test on Windows")
+	}
+
+	scenarios := []struct {
+		name           string
+		configLanguage string
+		envLanguage    string
+		expected       string
+		expectedErr    bool
+	}{
+		{
+			name:           "configLanguage is nl",
+			configLanguage: "nl",
+			envLanguage:    "en_US",
+			expected:       "nl",
+			expectedErr:    false,
+		},
+		{
+			name:           "configLanguage is an unsupported language",
+			configLanguage: "xy",
+			envLanguage:    "en_US",
+			expectedErr:    true,
+		},
+		{
+			name:           "auto-detection without LANG set",
+			configLanguage: "auto",
+			envLanguage:    "",
+			expected:       "en",
+			expectedErr:    false,
+		},
+		{
+			name:           "auto-detection with LANG set to nl_NL",
+			configLanguage: "auto",
+			envLanguage:    "nl_NL",
+			expected:       "nl",
+			expectedErr:    true, // Demonstrates the bug, this should be false
+		},
+		{
+			name:           "auto-detection with LANG set to zh-CN",
+			configLanguage: "auto",
+			envLanguage:    "zh-CN",
+			expected:       "zh-CN",
+			expectedErr:    false,
+		},
+		{
+			name:           "auto-detection with LANG set to an unsupported language",
+			configLanguage: "auto",
+			envLanguage:    "xy_XY",
+			expected:       "en",
+			expectedErr:    false,
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			log := newDummyLog()
+			t.Setenv("LANG", s.envLanguage)
+			actualTranslationSet, err := NewTranslationSetFromConfig(log, s.configLanguage)
+			if s.expectedErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+
+				expectedTranslationSet, _ := newTranslationSet(log, s.expected)
+				assert.Equal(t, expectedTranslationSet, actualTranslationSet)
+			}
+		})
+	}
+}