[cli-tests] Add --set-exact-output to update the expected output

`./run.py --set-exact-output` will update `stdout.expect` and
`stderr.expect` to match the expected output. This doesn't apply to
outputs which use `.glob` or `.ignore`.

tests/cli-tests/README.md

@@ -45,6 +45,16 @@ Examples:
 ./run.py --preserve --verbose basic/help.sh
 ```
 
+### Updating exact output
+
+If a test is failing because a `.stderr.exact` or `.stdout.exact` no longer matches, you can re-run the tests with `--set-exact-output` and the correct output will be written.
+
+Example:
+```
+./run.py --set-exact-output
+./run.py basic/help.sh --set-exact-output
+```
+
 ## Writing a test
 
 Test cases are arbitrary executables, and can be written in any language, but are generally shell scripts.

tests/cli-tests/run.py

@@ -209,6 +209,7 @@ class Options:
         preserve: bool,
         scratch_dir: str,
         test_dir: str,
+        set_exact_output: bool,
     ) -> None:
         self.env = env
         self.timeout = timeout
@@ -216,6 +217,7 @@ class Options:
         self.preserve = preserve
         self.scratch_dir = scratch_dir
         self.test_dir = test_dir
+        self.set_exact_output = set_exact_output
 
 
 class TestCase:
@@ -335,7 +337,7 @@ class TestCase:
             self._test_stdin.close()
             self._test_stdin = None
 
-    def _check_output_exact(self, out_name: str, expected: bytes) -> None:
+    def _check_output_exact(self, out_name: str, expected: bytes, exact_name: str) -> None:
         """
         Check the output named :out_name: for an exact match against the :expected: content.
         Saves the success and message.
@@ -349,6 +351,10 @@ class TestCase:
             self._success[check_name] = False
             self._message[check_name] = f"{out_name} does not match!\n> diff expected actual\n{diff(expected, actual)}"
 
+            if self._opts.set_exact_output:
+                with open(exact_name, "wb") as f:
+                    f.write(actual)
+
     def _check_output_glob(self, out_name: str, expected: bytes) -> None:
         """
         Check the output named :out_name: for a glob match against the :expected: glob.
@@ -386,7 +392,7 @@ class TestCase:
         ignore_name = f"{self._test_file}.{out_name}.ignore"
 
         if os.path.exists(exact_name):
-            return self._check_output_exact(out_name, read_file(exact_name))
+            return self._check_output_exact(out_name, read_file(exact_name), exact_name)
         elif os.path.exists(glob_name):
             return self._check_output_glob(out_name, read_file(glob_name))
         elif os.path.exists(ignore_name):
@@ -394,7 +400,7 @@ class TestCase:
             self._success[check_name] = True
             self._message[check_name] = f"{out_name} ignored!"
         else:
-            return self._check_output_exact(out_name, bytes())
+            return self._check_output_exact(out_name, bytes(), exact_name)
 
     def _check_stderr(self) -> None:
         """Checks the stderr output against the expectation."""
@@ -678,6 +684,11 @@ if __name__ == "__main__":
             "Scratch directory located in TEST_DIR/scratch/."
         )
     )
+    parser.add_argument(
+        "--set-exact-output",
+        action="store_true",
+        help="Set stderr.exact and stdout.exact for all failing tests, unless .ignore or .glob already exists"
+    )
     parser.add_argument(
         "tests",
         nargs="*",
@@ -714,6 +725,7 @@ if __name__ == "__main__":
         preserve=args.preserve,
         test_dir=args.test_dir,
         scratch_dir=scratch_dir,
+        set_exact_output=args.set_exact_output,
     )
 
     if len(args.tests) == 0: