Add testing for a config entity

Good find with the email grabbing utility function :) Looks like a solid patch, just relatively minor comments.

+++ b/lib/Drupal/config_translation/Tests/ConfigTranslationUITest.phpundefined
@@ -20,7 +20,14 @@ class ConfigTranslationUITest extends WebTestBase {
+  /**
+   * Languages to enable.
+   *
+   * @var array
+   */
+  protected $languages = array('fr', 'ta');
 

Make this $langcodes. $languages would be an array of language objects.

+++ b/lib/Drupal/config_translation/Tests/ConfigTranslationUITest.phpundefined
@@ -151,6 +166,60 @@ class ConfigTranslationUITest extends WebTestBase {
   /**
+   * Test case for site information translation interface.
+   */

Contact category translation, right? :)

+++ b/lib/Drupal/config_translation/Tests/ConfigTranslationUITest.phpundefined
@@ -151,6 +166,60 @@ class ConfigTranslationUITest extends WebTestBase {
+    // Check for default contact form config entity from Contact module.
+    $this->assertLinkByHref('admin/structure/contact/manage/feedback/edit');
+
+    // Visit page to check to update details and check for translation tab.
+    $this->assertLinkByHref('admin/structure/contact/manage/feedback/edit');

These two do the same thing? I think what you wanted is to go to 'contact/feedback' after the drupalPost below and check the original language versions?

+++ b/lib/Drupal/config_translation/Tests/ConfigTranslationUITest.phpundefined
@@ -151,6 +166,60 @@ class ConfigTranslationUITest extends WebTestBase {
+    // Keep it out of loop, as state() capture all emails.

// We get all emails so no need to check inside the loop.

+++ b/lib/Drupal/config_translation/Tests/ConfigTranslationUITest.phpundefined
@@ -151,6 +166,60 @@ class ConfigTranslationUITest extends WebTestBase {
+        // Needs trim as getting new line at end.

// Trim because we get an added newline for the body.

Thanks, committed.