Add warning when testpaths is set but paths are not found by glob (#11044)

Closes #11013

---------

Co-authored-by: Ran Benita <ran@unusedvar.com>

AUTHORS

@@ -197,6 +197,7 @@ Justice Ndou
 Justyna Janczyszyn
 Kale Kundert
 Kamran Ahmad
+Kenny Y
 Karl O. Pinc
 Karthikeyan Singaravelan
 Katarzyna Jachim

changelog/11013.improvement.rst

@@ -0,0 +1 @@
+Added warning when :confval:`testpaths` is set, but paths are not found by glob. In this case, pytest will fall back to searching from the current directory.

src/_pytest/config/__init__.py

@@ -1382,6 +1382,15 @@ class Config:
                         args = []
                         for path in testpaths:
                             args.extend(sorted(glob.iglob(path, recursive=True)))
+                        if testpaths and not args:
+                            warning_text = (
+                                "No files were found in testpaths; "
+                                "consider removing or adjusting your testpaths configuration. "
+                                "Searching recursively from the current directory instead."
+                            )
+                            self.issue_config_time_warning(
+                                PytestConfigWarning(warning_text), stacklevel=3
+                            )
                 if not args:
                     source = Config.ArgsSource.INCOVATION_DIR
                     args = [str(self.invocation_params.dir)]

testing/test_warnings.py

@@ -777,6 +777,20 @@ class TestStackLevel:
         )
 
 
+def test_warning_on_testpaths_not_found(pytester: Pytester) -> None:
+    # Check for warning when testpaths set, but not found by glob
+    pytester.makeini(
+        """
+        [pytest]
+        testpaths = absent
+        """
+    )
+    result = pytester.runpytest()
+    result.stdout.fnmatch_lines(
+        ["*ConfigWarning: No files were found in testpaths*", "*1 warning*"]
+    )
+
+
 def test_resource_warning(pytester: Pytester, monkeypatch: pytest.MonkeyPatch) -> None:
     # Some platforms (notably PyPy) don't have tracemalloc.
     # We choose to explicitly not skip this in case tracemalloc is not