[sheet-] in execCommand(), fail if cmd does not exist

During replay, if a command does not exist, failing is safer
than warning. A nonexistent command could be caused by a typo
in a user-edited command log, or previously user-defined commands
that no longer exist.

visidata/basesheet.py

@@ -194,7 +194,7 @@ def execCommand(self, longname, vdglobals=None, keystrokes=None):
 
         cmd = self.getCommand(longname or keystrokes)
         if not cmd:
-            vd.warning('no command for %s' % (longname or keystrokes))
+            vd.fail('no command for %s' % (longname or keystrokes))
             return False
 
         escaped = False

visidata/tests/test_commands.py

@@ -173,6 +173,10 @@ def runOneTest(self, mock_screen, longname):
 
         sample_file = vd.pkg_resources_files(visidata) / 'tests/sample.tsv'
         vs = visidata.TsvSheet('test_commands', source=visidata.Path(sample_file))
+        cmd = vs.getCommand(longname)
+        if not cmd:
+            vd.warning(f'command cannot be tested on TsvSheet, skipping:  {longname}')
+            return
         vs.reload.__wrapped__(vs)
         vs.vd = vd
         vd.sheets = [vs]