Engine: Add more tests for left and right ERB Trimming (marcoroth#650)

More tests for marcoroth#649 and marcoroth#841.

Author: marcoroth

examples/left-right-trim.html.erb

@@ -0,0 +1,3 @@
+<%- if true -%>
+  <h1>Content</h1>
+<%- end -%>

examples/left-trim.html.erb

@@ -0,0 +1,3 @@
+<%- if true %>
+  <h1>Content</h1>
+<%- end %>

examples/right-trim.html.erb

@@ -0,0 +1,3 @@
+<% if true -%>
+  <h1>Content</h1>
+<% end -%>

test/engine/evaluation_test.rb

@@ -434,5 +434,23 @@ class EvaluationTest < Minitest::Spec
 
       assert_evaluated_snapshot(template, { more: "ignored" }, { escape: false })
     end
+
+    test "left trim" do
+      template = File.read("examples/left-trim.html.erb")
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
+
+    test "right trim" do
+      template = File.read("examples/right-trim.html.erb")
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
+
+    test "left and right trim" do
+      template = File.read("examples/left-right-trim.html.erb")
+
+      assert_evaluated_snapshot(template, {}, { escape: false })
+    end
   end
 end