Reorganize unit tests based on discussion with Jim Edwards

My original idea had been to have a 'tests' subdirectory of each
production code directory, and to have unit tests live there. However,
Jim Edwards suggested having a top-level tests directory, and then
having a directory structure under that that mirrors the production code
directory structure. This commit does that.

Note that I have also moved case_fake.py to a higher level within the
tests directory, mirroring the location of case.py.

Test suite: python -m unittest discover -s CIME/tests -t .
Test baseline: N/A
Test namelist changes: N/A
Test status: pass

Fixes: None

User interface changes?: No

Code review: None

utils/python/CIME/tests/README

@@ -0,0 +1,6 @@
+The directory structure of this tests directory mirrors the directory structure
+of the parent (production code) directory.
+
+So, for example, unit tests for CIME/foo.py should live in
+CIME/tests/test_foo.py, and unit tests for CIME/SystemTests/bar.py should live
+in CIME/tests/SystemTests/test_bar.py.

utils/python/CIME/SystemTests/tests/test_system_tests_compare_two.py → utils/python/CIME/tests/SystemTests/test_system_tests_compare_two.py

@@ -12,7 +12,7 @@
 
 from CIME.SystemTests.system_tests_compare_two import SystemTestsCompareTwo
 import CIME.test_status as test_status
-from CIME.SystemTests.tests.case_fake import CaseFake
+from CIME.tests.case_fake import CaseFake
 
 # ========================================================================
 # Structure for storing information about calls made to methods

utils/python/CIME/SystemTests/tests/test_system_tests_compare_two_link_to_case2_output.py → utils/python/CIME/tests/SystemTests/test_system_tests_compare_two_link_to_case2_output.py

@@ -10,7 +10,7 @@
 import shutil
 import tempfile
 from CIME.SystemTests.system_tests_compare_two import SystemTestsCompareTwo
-from CIME.SystemTests.tests.case_fake import CaseFake
+from CIME.tests.case_fake import CaseFake
 
 # ========================================================================
 # Fake version of SystemTestsCompareTwo that overrides some functionality for

utils/python/CIME/SystemTests/tests/test_case_fake.py → utils/python/CIME/tests/test_case_fake.py

@@ -9,7 +9,7 @@
 import os
 import shutil
 
-from CIME.SystemTests.tests.case_fake import CaseFake
+from CIME.tests.case_fake import CaseFake
 
 class TestCaseFake(unittest.TestCase):
 

utils/python/tests/scripts_regression_tests.py

@@ -42,19 +42,21 @@ def test_resolve_variable_name(self):
                         msg="Path did not resolve to existing file %s" % machinefile)
 
     def test_unittests(self):
-        # Finds all files contained in LIB_DIR or its subdirectories that match
-        # the pattern 'test*.py', and runs the unit tests found there (i.e.,
-        # tests defined using python's unittest module).
+        # Finds all files contained in CIME/tests or its subdirectories that
+        # match the pattern 'test*.py', and runs the unit tests found there
+        # (i.e., tests defined using python's unittest module).
         #
         # This is analogous to running:
-        #     python -m unittest discover
+        #     python -m unittest discover -s CIME/tests -t .
+        # from cime/utils/python
         #
         # Yes, that means we have a bunch of unit tests run from this one unit
         # test.
 
         testsuite = unittest.defaultTestLoader.discover(
-            start_dir = LIB_DIR,
-            pattern = 'test*.py')
+            start_dir = os.path.join(LIB_DIR,"CIME","tests"),
+            pattern = 'test*.py',
+            top_level_dir = LIB_DIR)
 
         testrunner = unittest.TextTestRunner(buffer=False)