Clarify error message in case no collectors are found for a file

AUTHORS

@@ -325,6 +325,7 @@ Thomas Grainger
 Thomas Hisch
 Tim Hoffmann
 Tim Strazny
+Tobias Diez
 Tom Dalton
 Tom Viner
 Tomáš Gavenčiak

changelog/9823.improvement.rst

@@ -0,0 +1 @@
+Improved error message that is shown when no collector is found for a given file.

src/_pytest/main.py

@@ -645,9 +645,14 @@ def perform_collect(
             self.trace.root.indent -= 1
             if self._notfound:
                 errors = []
-                for arg, cols in self._notfound:
-                    line = f"(no name {arg!r} in any of {cols!r})"
-                    errors.append(f"not found: {arg}\n{line}")
+                for arg, collectors in self._notfound:
+                    if collectors:
+                        errors.append(
+                            f"not found: {arg}\n(no name {arg!r} in any of {collectors!r})"
+                        )
+                    else:
+                        errors.append(f"found no collectors for {arg}")
+
                 raise UsageError(*errors)
             if not genitems:
                 items = rep.result

testing/acceptance_test.py

@@ -186,8 +186,7 @@ def test_not_collectable_arguments(self, pytester: Pytester) -> None:
         assert result.ret == ExitCode.USAGE_ERROR
         result.stderr.fnmatch_lines(
             [
-                f"ERROR: not found: {p2}",
-                f"(no name {str(p2)!r} in any of [[][]])",
+                f"ERROR: found no collectors for {p2}",
                 "",
             ]
         )

testing/test_config.py

@@ -1855,8 +1855,7 @@ def test_config_blocked_default_plugins(pytester: Pytester, plugin: str) -> None
         assert result.ret == ExitCode.USAGE_ERROR
         result.stderr.fnmatch_lines(
             [
-                "ERROR: not found: */test_config_blocked_default_plugins.py",
-                "(no name '*/test_config_blocked_default_plugins.py' in any of [])",
+                "ERROR: found no collectors for */test_config_blocked_default_plugins.py",
             ]
         )
         return