Added COMMON folder for tests

A COMMON folder allows code reuse across different test cases. This
avoids code duplication or code enterying the application space.

The COMMON folder is uppercase to match naming conventions in Mbed OS.

tools/test_api.py

@@ -28,6 +28,7 @@ import argparse
 import datetime
 import threading
 import ctypes
+import functools
 from types import ListType
 from colorama import Fore, Back, Style
 from prettytable import PrettyTable
@@ -71,7 +72,6 @@ from tools.utils import argparse_filestring_type
 from tools.utils import argparse_uppercase_type
 from tools.utils import argparse_lowercase_type
 from tools.utils import argparse_many
-from tools.utils import get_path_depth
 
 import tools.host_tests.host_tests_plugins as host_tests_plugins
 
@@ -2019,9 +2019,15 @@ def find_tests(base_dir, target_name, toolchain_name, app_config=None):
     toolchain_name: name of the toolchain to use for scanning (ex. 'GCC_ARM')
     options: Compile options to pass to the toolchain (ex. ['debug-info'])
     app_config - location of a chosen mbed_app.json file
+
+    returns a dictionary where keys are the test name, and the values are
+    lists of paths needed to biuld the test.
     """
 
+    # Temporary structure: tests referenced by (name, base, group, case) tuple
     tests = {}
+    # List of common folders: (predicate function, path) tuple
+    commons = []
 
     # Prepare the toolchain
     toolchain = prepare_toolchain([base_dir], None, target_name, toolchain_name,
@@ -2042,32 +2048,52 @@ def find_tests(base_dir, target_name, toolchain_name, app_config=None):
             # Loop through all subdirectories
             for d in test_resources.inc_dirs:
 
-                # If the test case folder is not called 'host_tests' and it is
+                # If the test case folder is not called 'host_tests' or 'COMMON' and it is
                 # located two folders down from the main 'TESTS' folder (ex. TESTS/testgroup/testcase)
                 # then add it to the tests
-                path_depth = get_path_depth(relpath(d, walk_base_dir))
-                if path_depth == 2:
+                relative_path = relpath(d, walk_base_dir)
+                relative_path_parts = os.path.normpath(relative_path).split(os.sep)
+                if len(relative_path_parts) == 2:
                     test_group_directory_path, test_case_directory = os.path.split(d)
                     test_group_directory = os.path.basename(test_group_directory_path)
 
-                    # Check to make sure discoverd folder is not in a host test directory
-                    if test_case_directory != 'host_tests' and test_group_directory != 'host_tests':
+                    # Check to make sure discoverd folder is not in a host test directory or common directory
+                    special_dirs = ['host_tests', 'COMMON']
+                    if test_group_directory not in special_dirs and test_case_directory not in special_dirs:
                         test_name = test_path_to_name(d, base_dir)
-                        tests[test_name] = d
+                        tests[(test_name, walk_base_dir, test_group_directory, test_case_directory)] = [d]
 
-    return tests
+                # Also find any COMMON paths, we'll add these later once we find all the base tests
+                if 'COMMON' in relative_path_parts:
+                    if relative_path_parts[0] != 'COMMON':
+                        def predicate(base_pred, group_pred, (name, base, group, case)):
+                            return base == base_pred and group == group_pred
+                        commons.append((functools.partial(predicate, walk_base_dir, relative_path_parts[0]), d))
+                    else:
+                        def predicate(base_pred, (name, base, group, case)):
+                            return base == base_pred
+                        commons.append((functools.partial(predicate, walk_base_dir), d))
+
+    # Apply common directories
+    for pred, path in commons:
+        for test_identity, test_paths in tests.iteritems():
+            if pred(test_identity):
+                test_paths.append(path)
+
+    # Drop identity besides name
+    return {name: paths for (name, _, _, _), paths in tests.iteritems()}
 
 def print_tests(tests, format="list", sort=True):
     """Given a dictionary of tests (as returned from "find_tests"), print them
     in the specified format"""
     if format == "list":
         for test_name in sorted(tests.keys()):
-            test_path = tests[test_name]
+            test_path = tests[test_name][0]
             print "Test Case:"
             print "    Name: %s" % test_name
             print "    Path: %s" % test_path
     elif format == "json":
-        print json.dumps(tests, indent=2)
+        print json.dumps({test_name: test_path[0] for test_name, test_paths in tests}, indent=2)
     else:
         print "Unknown format '%s'" % format
         sys.exit(1)
@@ -2164,13 +2190,16 @@ def build_tests(tests, base_source_paths, build_path, target, toolchain_name,
     jobs_count = int(jobs if jobs else cpu_count())
     p = Pool(processes=jobs_count)
     results = []
-    for test_name, test_path in tests.iteritems():
-        test_build_path = os.path.join(build_path, test_path)
-        src_path = base_source_paths + [test_path]
-        bin_file = None
-        test_case_folder_name = os.path.basename(test_path)
+    for test_name, test_paths in tests.iteritems():
+        if type(test_paths) != ListType:
+            test_paths = [test_paths]
 
-        args = (src_path, test_build_path, target, toolchain_name)
+        test_build_path = os.path.join(build_path, test_paths[0])
+        src_paths = base_source_paths + test_paths
+        bin_file = None
+        test_case_folder_name = os.path.basename(test_paths[0])
+
+        args = (src_paths, test_build_path, target, toolchain_name)
         kwargs = {
             'jobs': 1,
             'clean': clean,