compile_and_test_for_board: Add only-if-changed feature

This will use the make test-input-hash-changed feature to save
the test hashes with the results and optionally skip running
the test if nothing has changed.

Murdock already has this feature but it is not easily accessible.

This should prevent unneeded flash cycles as well as speeding up
constant rerunning of tests for boards.

dist/tools/compile_and_test_for_board/compile_and_test_for_board.py

@@ -44,6 +44,7 @@ usage: compile_and_test_for_board.py [-h] [--applications APPLICATIONS]
                                      [--test-targets TEST_TARGETS]
                                      [--test-available-targets TEST_AVAILABLE_TARGETS]
                                      [--report-xml] [--jobs JOBS]
+                                     [--only-if-changed]
                                      riot_directory board [result_directory]
 
 positional arguments:
@@ -84,6 +85,9 @@ optional arguments:
                         (default: False)
   --jobs JOBS, -j JOBS  Parallel building (0 means not limit, like '--jobs')
                         (default: None)
+  --only-if-changed, -c
+                        Only test if the application has changed since last
+                        test (default: False)
 ```
 """  # noqa
 
@@ -225,6 +229,7 @@ def is_in_directory(path, directory):
     return path.startswith(directory)
 
 
+# pylint: disable=too-many-instance-attributes
 class RIOTApplication:
     """RIOT Application representation.
 
@@ -245,6 +250,7 @@ class RIOTApplication:
     )
     FLASH_TARGETS = ("flash-only",)
     TEST_TARGETS = ("test",)
+    TEST_INPUT_HASH = ("test-input-hash-changed",)
     TEST_AVAILABLE_TARGETS = ("test/available",)
 
     # pylint: disable=too-many-arguments
@@ -252,6 +258,7 @@ class RIOTApplication:
         self.board = board
         self.riotdir = riotdir
         self.appdir = appdir
+        self.hashdir = os.path.abspath(os.path.join(resultdir, "hashes", appdir))
         self.resultdir = os.path.join(resultdir, appdir)
         if junit:
             if not junit_xml:
@@ -368,8 +375,11 @@ class RIOTApplication:
         incremental=False,
         jobs=False,
         with_test_only=False,
+        only_if_changed=False,
     ):
         # pylint:disable=too-many-arguments
+        # pylint:disable=too-many-nested-blocks
+        # pylint:disable=too-many-branches
         """Compile and execute test if available.
 
         Checks for board supported/enough memory, compiles.
@@ -422,8 +432,28 @@ class RIOTApplication:
         if clean_after:
             self.clean_intermediates()
 
+        # pylint: disable=too-many-nested-blocks
         if runtest:
             if has_test:
+                if only_if_changed:
+                    try:
+                        out = self.make(
+                            self.TEST_INPUT_HASH,
+                            env={"RIOT_TEST_HASH_DIR": self.hashdir},
+                        )
+                        hash_match = "hashes match" in out.lower()
+                        self.logger.info("Hashes match: %r", hash_match)
+                        if hash_match:
+                            self._skip(
+                                "bins_unchanged",
+                                f"{self.appdir} matched test input hashes.",
+                            )
+                            if clean_after:
+                                self.clean()
+                            self.logger.info("Success")
+                            return
+                    except subprocess.CalledProcessError as err:
+                        self._make_handle_error(self.TEST_INPUT_HASH[0], err)
                 setuptasks = collections.OrderedDict([("flash", self.FLASH_TARGETS)])
                 self.make_with_outfile(
                     "test", self.TEST_TARGETS, save_output=True, setuptasks=setuptasks
@@ -732,7 +762,6 @@ PARSER.add_argument(
     default=False,
     help="Output results to report.xml in the " "result_directory",
 )
-
 PARSER.add_argument(
     "--jobs",
     "-j",
@@ -740,6 +769,14 @@ PARSER.add_argument(
     default=None,
     help="Parallel building (0 means not limit, like '--jobs')",
 )
+# Arg that allows hashes of tests to be saved locally in a hashes folder
+# and used to skip tests if new hashes match.
+PARSER.add_argument(
+    "--only-if-changed",
+    "-c",
+    action="store_true",
+    help="Only test if the application has changed since last test",
+)
 
 
 def main(args):
@@ -798,6 +835,7 @@ def main(args):
             incremental=args.incremental,
             jobs=args.jobs,
             with_test_only=args.with_test_only,
+            only_if_changed=args.only_if_changed,
         )
         for app in applications
     ]