Add more tests and docs

changelog/7346.feature.rst

@@ -0,0 +1 @@
+Version information as defined by `PEP 440 <https://www.python.org/dev/peps/pep-0440/#version-specifiers>`_ may now be included when providing plugins to the ``required_plugins`` configuration option.

doc/en/reference.rst

@@ -1562,12 +1562,14 @@ passed multiple times. The expected format is ``name=value``. For example::
 .. confval:: required_plugins
 
    A space separated list of plugins that must be present for pytest to run.
+   Plugins can be listed with or without version specifiers directly following
+   their name. Whitespace between different version specifiers is not allowed.
    If any one of the plugins is not found, emit an error.
 
    .. code-block:: ini
 
        [pytest]
-       required_plugins = pytest-html pytest-xdist
+       required_plugins = pytest-django>=3.0.0,<4.0.0 pytest-html pytest-xdist>=1.0.0
 
 
 .. confval:: testpaths

src/_pytest/config/__init__.py

@@ -1101,7 +1101,7 @@ class Config:
         plugin_info = self.pluginmanager.list_plugin_distinfo()
         plugin_dist_info = {dist.project_name: dist.version for _, dist in plugin_info}
 
-        missing_plugins = ["a"]
+        missing_plugins = []
         for required_plugin in required_plugins:
             spec = None
             try:

testing/test_config.py

@@ -265,6 +265,13 @@ class TestParseIni:
             (
                 """
           [pytest]
+          required_plugins = pytest-xdist>1.0.0,<2.0.0
+          """,
+                "",
+            ),
+            (
+                """
+          [pytest]
           required_plugins = pytest-xdist~=1.32.0 pytest-xdist==1.32.0 pytest-xdist!=0.0.1 pytest-xdist<=99.99.0
             pytest-xdist>=1.32.0 pytest-xdist<9.9.9 pytest-xdist>1.30.0 pytest-xdist===1.32.0
           """,
@@ -280,16 +287,9 @@ class TestParseIni:
             (
                 """
           [pytest]
-          required_plugins = pytest-xdist==aegsrgrsgs
+          required_plugins = pytest-xdist==aegsrgrsgs pytest-xdist==-1 pytest-xdist>2.1.1,>3.0.0
           """,
-                "Missing required plugins: pytest-xdist==aegsrgrsgs",
+                "Missing required plugins: pytest-xdist==-1, pytest-xdist==aegsrgrsgs, pytest-xdist>2.1.1,>3.0.0",
-            ),
-            (
-                """
-          [pytest]
-          required_plugins = pytest-xdist==-1
-          """,
-                "Missing required plugins: pytest-xdist==-1",
             ),
             (
                 """