fix(run): improve error when command not found (#5243)

src/poetry/console/commands/run.py

@@ -29,7 +29,11 @@ class RunCommand(EnvCommand):
         if scripts and script in scripts:
         if scripts and script in scripts:
             return self.run_script(scripts[script], args)
             return self.run_script(scripts[script], args)
 
 
-        return self.env.execute(*args)
+        try:
+            return self.env.execute(*args)
+        except FileNotFoundError:
+            self.line_error(f"<error>Command not found: <c1>{script}</c1></error>")
+            return 1
 
 
     @property
     @property
     def _module(self) -> "Module":
     def _module(self) -> "Module":

tests/console/commands/test_run.py

@@ -37,3 +37,14 @@ def test_run_keeps_options_passed_before_command(
         app_tester.application.long_version + "\n"
         app_tester.application.long_version + "\n"
     )
     )
     assert [] == env.executed
     assert [] == env.executed
+
+
+def test_run_has_helpful_error_when_command_not_found(
+    app_tester: "ApplicationTester", env: "MockEnv"
+):
+    env._execute = True
+    app_tester.execute("run nonexistent-command")
+
+    assert env.executed == [["nonexistent-command"]]
+    assert app_tester.status_code == 1
+    assert app_tester.io.fetch_error() == "Command not found: nonexistent-command\n"