Merge pull request #7 from catalyst/fix-fail-unit-test-plot

Fix unit test of plots within the radio input type.

tests/input_radio_test.php

@@ -354,7 +354,9 @@ public function test_radio_plots() {
         // @codingStandardsIgnoreEnd
         $render = $el->render(new stack_input_state(
                 stack_input::SCORE, array('2'), '', '', '', '', ''), 'stack1__ans1', false, null);
-        $this->assertTrue(is_int(strpos($render, "<img src='https://www.example.com/moodle/question/type/stack/plot.php")));
+        // We don't test for the < at the start of the img tag as this is now protected as &lt; in the render.
+        // However, the plot system does not use the LaTeX.
+        $this->assertTrue(is_int(strpos($render, "img src='https://www.example.com/moodle/question/type/stack/plot.php")));
         $this->assertTrue(is_int(strpos($render,
                 "alt='STACK auto-generated plot of x with parameters [[x,-2,2],[y,-3,3]]'")));
         $this->assertTrue(is_int(strpos($render,