refactor: move xmodule folder to root

- Moving xmodule folder to root as we're dissolving sub-projects of common folder in edx-platform
    - More info: https://openedx.atlassian.net/browse/BOM-2579
- -e common/lib/xmodule has been removed from the requirements as xmodule has itself become the part of edx-platform and not being installed through requirements
- The test files common/lib/xmodule/test_files/ have been removed as they are not being used anymore

xmodule/tests/test_unit_block.py

@@ -0,0 +1,87 @@
+"""
+Tests for the Unit XBlock
+"""
+
+import re
+import unittest
+from xml.dom import minidom
+from unittest.mock import patch
+
+from web_fragments.fragment import Fragment
+from xblock.core import XBlock
+from xblock.completable import XBlockCompletionMode
+from xblock.test.test_parsing import XmlTest
+
+from xmodule.unit_block import UnitBlock
+
+
+class FakeHTMLBlock(XBlock):
+    """ An HTML block for use in tests """
+    def student_view(self, context=None):  # pylint: disable=unused-argument
+        """Provide simple HTML student view."""
+        return Fragment("This is some HTML.")
+
+
+class FakeVideoBlock(XBlock):
+    """ A video block for use in tests """
+    def student_view(self, context=None):  # pylint: disable=unused-argument
+        """Provide simple Video student view."""
+        return Fragment(
+            '<iframe width="560" height="315" src="https://www.youtube.com/embed/B-EFayAA5_0"'
+            ' frameborder="0" allow="autoplay; encrypted-media"></iframe>'
+        )
+
+
+class UnitBlockTests(XmlTest, unittest.TestCase):
+    """
+    Tests of the Unit XBlock.
+
+    There's not much to this block, so we keep it simple.
+    """
+    maxDiff = None
+
+    @XBlock.register_temp_plugin(FakeHTMLBlock, identifier='fake-html')
+    @XBlock.register_temp_plugin(FakeVideoBlock, identifier='fake-video')
+    def test_unit_html(self):
+        block = self.parse_xml_to_block("""\
+            <unit>
+                <fake-html/>
+                <fake-video/>
+            </unit>
+        """)
+
+        with patch.object(block.runtime, 'applicable_aside_types', return_value=[]):  # Disable problematic Acid aside
+            html = block.runtime.render(block, 'student_view').content
+
+        self.assertXmlEqual(html, (
+            '<div class="xblock-v1 xblock-v1-student_view" data-usage="u_1" data-block-type="unit">'
+            '<div class="unit-xblock vertical">'
+            '<div class="xblock-v1 xblock-v1-student_view" data-usage="u_3" data-block-type="fake-html">'
+            'This is some HTML.'
+            '</div>'
+            '<div class="xblock-v1 xblock-v1-student_view" data-usage="u_5" data-block-type="fake-video">'
+            '<iframe width="560" height="315" src="https://www.youtube.com/embed/B-EFayAA5_0"'
+            ' frameborder="0" allow="autoplay; encrypted-media"></iframe>'
+            '</div>'
+            '</div>'
+            '</div>'
+        ))
+
+    def test_is_aggregator(self):
+        """
+        The unit XBlock is designed to hold other XBlocks, so check that its
+        completion status is defined as the aggregation of its child blocks.
+        """
+        assert XBlockCompletionMode.get_mode(UnitBlock) == XBlockCompletionMode.AGGREGATOR
+
+    def assertXmlEqual(self, xml_str_a, xml_str_b):
+        """
+        Assert that the given XML strings are equal,
+        ignoring attribute order and some whitespace variations.
+        """
+        def clean(xml_str):
+            # Collapse repeated whitespace:
+            xml_str = re.sub(r'(\s)\s+', r'\1', xml_str)
+            xml_bytes = xml_str.encode('utf8')
+            return minidom.parseString(xml_bytes).toprettyxml()
+        assert clean(xml_str_a) == clean(xml_str_b)