Fixed broken Selenium test

The test is broken on beta cluster because the formula is rendered as
meta tag. It is rendered at img tag on my mediawiki-vagrant virtual
machine. The test now works on both environments.

Bug: T128190
Change-Id: I458d618af24533d104fcac25a8d8c6468b14605a

tests/browser/features/math.feature

@@ -5,6 +5,4 @@ Feature: Math
     Given I am editing a random page with source editor
     When I type <math>3 + 2</math>
       And I click Preview
-    Then the page should contain an img tag
-      And alt for that img should be 3 + 2
-      And src for that img should contain /math/
+    Then the page should contain 3 + 2 image

tests/browser/features/step_definitions/math_steps.rb

@@ -10,14 +10,6 @@ When(/^I type (.+)$/) do |write_text|
   on(EditPage).article_text = write_text
 end
 
-Then(/^alt for that img should be (.+)$/) do |alt|
-  expect(on(EditPage).math_image_element.element.alt).to eq(alt)
-end
-
-Then(/^src for that img should contain (.+)$/) do |src|
-  expect(on(EditPage).math_image_element.element.src).to match Regexp.escape src
-end
-
-Then(/^the page should contain an img tag$/) do
+Then(/^the page should contain 3 \+ 2 image$/) do
   expect(on(EditPage).math_image_element.when_present).to be_visible
 end

tests/browser/features/support/pages/edit_page.rb

@@ -4,6 +4,13 @@ class EditPage
   page_url 'Special:Random?action=edit'
 
   text_area(:article_text, id: 'wpTextbox1')
-  img(:math_image, class: 'tex')
   button(:preview, id: 'wpPreview')
+
+  def math_image_element
+    if env.lookup(:mediawiki_environment, default: nil) == 'beta'
+      browser.meta(class: 'mwe-math-fallback-image-inline')
+    else
+      browser.img(class: 'tex')
+    end
+  end
 end