Minimize number of tests that fail on core branch.

tools/test_check.py

 #! /usr/bin/env python
 
+"""
+Unit and functional tests for markdown lesson template validator.
+
+Some of these tests require looking for example files, which exist only on
+the gh-pages branch.   Some tests may therefore fail on branch "core".
+"""
+
+
 import imp
 import logging
 import os
@@ -91,13 +99,33 @@ keywords: this is not a list
     # TESTS INVOLVING SECTION TITLES/HEADINGS
     def test_index_has_valid_section_headings(self):
         """The provided index page"""
-        sample_validator = self.VALIDATOR(self.SAMPLE_FILE)
-        res = sample_validator._validate_section_heading_order()
+        validator = self._create_validator("""## Topics
+
+1.  [Topic Title One](01-one.html)
+2.  [Topic Title Two](02-two.html)
+
+## Other Resources
+
+*   [Motivation](motivation.html)
+*   [Reference Guide](reference.html)
+*   [Next Steps](discussion.html)
+*   [Instructor's Guide](instructors.html)""")
+        res = validator._validate_section_heading_order()
         self.assertTrue(res)
 
     def test_index_fail_when_section_heading_absent(self):
-        sample_validator = self.VALIDATOR(self.SAMPLE_FILE)
-        res = sample_validator.ast.has_section_heading("Fake heading")
+        validator = self._create_validator("""## Topics
+
+1.  [Topic Title One](01-one.html)
+2.  [Topic Title Two](02-two.html)
+
+## Other Resources
+
+*   [Motivation](motivation.html)
+*   [Reference Guide](reference.html)
+*   [Next Steps](discussion.html)
+*   [Instructor's Guide](instructors.html)""")
+        res = validator.ast.has_section_heading("Fake heading")
         self.assertFalse(res)
 
     def test_fail_when_section_heading_is_wrong_level(self):
@@ -185,12 +213,15 @@ Paragraph of introductory material.
 
     # TESTS INVOLVING LINKS TO OTHER CONTENT
     def test_file_links_validate(self):
+        """Verify that all links in a sample file validate.
+        Involves checking for example files; may fail on "core" branch"""
         sample_validator = self.VALIDATOR(self.SAMPLE_FILE)
         res = sample_validator._validate_links()
         self.assertTrue(res)
 
     def test_html_link_to_extant_md_file_passes(self):
-        """Verify that an HTML link with corresponding MD file will pass"""
+        """Verify that an HTML link with corresponding MD file will pass
+        Involves checking for example files; may fail on "core" branch"""
         validator = self._create_validator("""[Topic Title One](01-one.html)""")
         self.assertTrue(validator._validate_links())
 
@@ -199,6 +230,8 @@ Paragraph of introductory material.
 
         For now this just tests that the regex handles #anchors.
          It doesn't validate that the named anchor exists in the md file
+
+        Involves checking for example files; may fail on "core" branch
         """
         validator = self._create_validator("""[Topic Title One](01-one.html#anchor)""")
         self.assertTrue(validator._validate_links())
@@ -230,7 +263,8 @@ SQLite uses the integers 0 and 1 for the former, and represents the latter as di
         self.assertFalse(validator._validate_links())
 
     def test_finds_image_asset(self):
-        """Image asset is found"""
+        """Image asset is found in the expected file location
+        Involves checking for example files; may fail on "core" branch"""
         validator = self._create_validator(
             """![this is the image's title](fig/example.svg "this is the image's alt text")""")
         self.assertTrue(validator._validate_links())
@@ -242,7 +276,9 @@ SQLite uses the integers 0 and 1 for the former, and represents the latter as di
         self.assertFalse(validator._validate_links())
 
     def test_non_html_link_finds_csv(self):
-        """Look for CSV file in appropriate folder"""
+        """Look for CSV file in appropriate folder
+        Involves checking for example files; may fail on "core" branch
+        """
         validator = self._create_validator(
             """Use [this CSV](data/data.csv) for the exercise.""")
         self.assertTrue(validator._validate_links())