Pass importmode to import_path in DoctestModule

This allows doctest to be used with namespace modules

changelog/3396.improvement.rst

@@ -0,0 +1 @@
+Doctests now respect the ``--import-mode`` flag.

src/_pytest/doctest.py

@@ -542,7 +542,11 @@ def _find(
             )
         else:
             try:
-                module = import_path(self.path, root=self.config.rootpath)
+                module = import_path(
+                    self.path,
+                    root=self.config.rootpath,
+                    mode=self.config.getoption("importmode"),
+                )
             except ImportError:
                 if self.config.getvalue("doctest_ignore_import_errors"):
                     pytest.skip("unable to import module %r" % self.path)

testing/test_doctest.py

@@ -113,6 +113,28 @@ def test_simple_doctestfile(self, pytester: Pytester):
         reprec = pytester.inline_run(p)
         reprec.assertoutcome(failed=1)
 
+    def test_importmode(self, pytester: Pytester):
+        p = pytester.makepyfile(
+            **{
+                "namespacepkg/innerpkg/__init__.py": "",
+                "namespacepkg/innerpkg/a.py": """
+                  def some_func():
+                    return 42
+                """,
+                "namespacepkg/innerpkg/b.py": """
+                  from namespacepkg.innerpkg.a import some_func
+                  def my_func():
+                    '''
+                    >>> my_func()
+                    42
+                    '''
+                    return some_func()
+                """,
+            }
+        )
+        reprec = pytester.inline_run(p, "--doctest-modules", "--import-mode=importlib")
+        reprec.assertoutcome(passed=1)
+
     def test_new_pattern(self, pytester: Pytester):
         p = pytester.maketxtfile(
             xdoc="""