Improve error message for cylc cat-log (#5830)

Improve error message for Cylc cat log

* replaced functional with integration tests for cat log error handling.

Author: wxtim

cylc/flow/scripts/cat_log.py

@@ -401,6 +401,17 @@ def main(
     options: 'Values',
     *ids,
     color: bool = False
+):
+    """Wrapper around the main script for simpler testing.
+    """
+    _main(parser, options, *ids, color=color)
+
+
+def _main(
+    parser: COP,
+    options: 'Values',
+    *ids,
+    color: bool = False
 ) -> None:
     """Implement cylc cat-log CLI.
 
@@ -481,10 +492,16 @@ def main(
                 ),
                 reverse=True
             )
-            try:
-                log_file_path = Path(logs[rotation_number])
-            except IndexError:
-                raise InputError("max rotation %d" % (len(logs) - 1))
+            if logs:
+                try:
+                    log_file_path = Path(logs[rotation_number])
+                except IndexError:
+                    raise InputError(
+                        f"--rotation {rotation_number} invalid "
+                        f"(max value is {len(logs) - 1})"
+                    )
+            else:
+                raise InputError('Log file not found.')
         else:
             log_file_path = Path(log_dir, file_name)
 

tests/functional/cylc-cat-log/03-bad-workflow.t

@@ -0,0 +1,97 @@
+# THIS FILE IS PART OF THE CYLC WORKFLOW ENGINE.
+# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""Integration test for the cat log script.
+"""
+
+import pytest
+import re
+import shutil
+from types import SimpleNamespace
+
+from cylc.flow.exceptions import InputError
+from cylc.flow.option_parsers import Options
+from cylc.flow.scripts.cat_log import (
+    _main as cat_log,
+    get_option_parser as cat_log_gop
+)
+
+
+BAD_NAME = "NONEXISTENTWORKFLOWNAME"
+
+
+@pytest.fixture
+def brokendir(run_dir):
+    brokendir = (run_dir / BAD_NAME)
+    brokendir.mkdir(exist_ok=True)
+    yield brokendir
+    shutil.rmtree(brokendir)
+
+
+def test_fail_no_file(flow):
+    """It produces a helpful error if there is no workflow log file.
+    """
+    parser = cat_log_gop()
+    id_ = flow({})
+    with pytest.raises(InputError, match='Log file not found.'):
+        cat_log(parser, Options(parser)(), id_)
+
+
+def test_fail_rotation_out_of_range(flow):
+    """It produces a helpful error if rotation number > number of log files.
+    """
+    parser = cat_log_gop()
+    id_ = flow({})
+    path = flow.args[1]
+    name = id_.split('/')[-1]
+    logpath = (path / name / 'log/scheduler')
+    logpath.mkdir(parents=True)
+    (logpath / '01-start-01.log').touch()
+
+    with pytest.raises(SystemExit):
+        cat_log(parser, Options(parser)(rotation_num=0), id_)
+
+    msg = r'--rotation 1 invalid \(max value is 0\)'
+
+    with pytest.raises(InputError, match=msg):
+        cat_log(parser, Options(parser)(rotation_num=1), id_)
+
+
+def test_bad_workflow(run_dir):
+    """Test "cylc cat-log" with bad workflow name."""
+    parser = cat_log_gop()
+    msg = re.compile(
+        fr'^Workflow ID not found: {BAD_NAME}'
+        fr'\n\(Directory not found: {run_dir}/{BAD_NAME}\)$',
+        re.MULTILINE
+    )
+    with pytest.raises(InputError, match=msg):
+        cat_log(parser, Options(parser)(filename='l'), BAD_NAME)
+
+
+def test_bad_workflow2(run_dir, brokendir, capsys):
+    """Check a non existent file in a valid workflow results in error.
+    """
+    parser = cat_log_gop()
+    with pytest.raises(SystemExit, match='1'):
+        cat_log(
+            parser,
+            Options(parser)(filename='j'),
+            BAD_NAME
+        )
+    msg = (
+        f'file not found: {run_dir}'
+        '/NONEXISTENTWORKFLOWNAME/log/j\n')
+    assert capsys.readouterr().err == msg