diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index d9abc17b4..ff6aee744 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -840,7 +840,7 @@ class Config:
             self.cache = None  # type: Optional[Cache]
 
     @property
-    def invocation_dir(self):
+    def invocation_dir(self) -> py.path.local:
         """Backward compatibility"""
         return py.path.local(str(self.invocation_params.dir))
 
diff --git a/src/_pytest/doctest.py b/src/_pytest/doctest.py
index 50f115cd1..026476b8a 100644
--- a/src/_pytest/doctest.py
+++ b/src/_pytest/doctest.py
@@ -7,6 +7,7 @@ import traceback
 import warnings
 from contextlib import contextmanager
 from typing import Dict
+from typing import Iterable
 from typing import List
 from typing import Optional
 from typing import Sequence
@@ -109,13 +110,18 @@ def pytest_unconfigure() -> None:
     RUNNER_CLASS = None
 
 
-def pytest_collect_file(path: py.path.local, parent):
+def pytest_collect_file(
+    path: py.path.local, parent
+) -> Optional[Union["DoctestModule", "DoctestTextfile"]]:
     config = parent.config
     if path.ext == ".py":
         if config.option.doctestmodules and not _is_setup_py(path):
-            return DoctestModule.from_parent(parent, fspath=path)
+            mod = DoctestModule.from_parent(parent, fspath=path)  # type: DoctestModule
+            return mod
     elif _is_doctest(config, path, parent):
-        return DoctestTextfile.from_parent(parent, fspath=path)
+        txt = DoctestTextfile.from_parent(parent, fspath=path)  # type: DoctestTextfile
+        return txt
+    return None
 
 
 def _is_setup_py(path: py.path.local) -> bool:
@@ -365,7 +371,7 @@ def _get_continue_on_failure(config):
 class DoctestTextfile(pytest.Module):
     obj = None
 
-    def collect(self):
+    def collect(self) -> Iterable[DoctestItem]:
         import doctest
 
         # inspired by doctest.testfile; ideally we would use it directly,
@@ -444,7 +450,7 @@ def _patch_unwrap_mock_aware():
 
 
 class DoctestModule(pytest.Module):
-    def collect(self):
+    def collect(self) -> Iterable[DoctestItem]:
         import doctest
 
         class MockAwareDocTestFinder(doctest.DocTestFinder):
diff --git a/src/_pytest/hookspec.py b/src/_pytest/hookspec.py
index 8b4505691..1321eff54 100644
--- a/src/_pytest/hookspec.py
+++ b/src/_pytest/hookspec.py
@@ -6,6 +6,7 @@ from typing import Optional
 from typing import Tuple
 from typing import Union
 
+import py.path
 from pluggy import HookspecMarker
 
 from .deprecated import COLLECT_DIRECTORY_HOOK
@@ -20,9 +21,14 @@ if TYPE_CHECKING:
     from _pytest.config import _PluggyPlugin
     from _pytest.config.argparsing import Parser
     from _pytest.main import Session
+    from _pytest.nodes import Collector
+    from _pytest.nodes import Item
     from _pytest.python import Metafunc
+    from _pytest.python import Module
+    from _pytest.python import PyCollector
     from _pytest.reports import BaseReport
 
+
 hookspec = HookspecMarker("pytest")
 
 # -------------------------------------------------------------------------
@@ -249,7 +255,7 @@ def pytest_collect_directory(path, parent):
     """
 
 
-def pytest_collect_file(path, parent):
+def pytest_collect_file(path: py.path.local, parent) -> "Optional[Collector]":
     """ return collection Node or None for the given path. Any new node
     needs to have the specified ``parent`` as a parent.
 
@@ -289,7 +295,7 @@ def pytest_make_collect_report(collector):
 
 
 @hookspec(firstresult=True)
-def pytest_pycollect_makemodule(path, parent):
+def pytest_pycollect_makemodule(path: py.path.local, parent) -> "Optional[Module]":
     """ return a Module collector or None for the given path.
     This hook will be called for each matching test module path.
     The pytest_collect_file hook needs to be used if you want to
@@ -302,7 +308,9 @@ def pytest_pycollect_makemodule(path, parent):
 
 
 @hookspec(firstresult=True)
-def pytest_pycollect_makeitem(collector, name, obj):
+def pytest_pycollect_makeitem(
+    collector: "PyCollector", name: str, obj
+) -> "Union[None, Item, Collector, List[Union[Item, Collector]]]":
     """ return custom item/collector for a python object in a module, or None.
 
     Stops at first non-None result, see :ref:`firstresult` """
diff --git a/src/_pytest/main.py b/src/_pytest/main.py
index 4eb47be2c..a0007d226 100644
--- a/src/_pytest/main.py
+++ b/src/_pytest/main.py
@@ -7,9 +7,11 @@ import sys
 from typing import Callable
 from typing import Dict
 from typing import FrozenSet
+from typing import Iterator
 from typing import List
 from typing import Optional
 from typing import Sequence
+from typing import Set
 from typing import Tuple
 from typing import Union
 
@@ -18,12 +20,14 @@ import py
 
 import _pytest._code
 from _pytest import nodes
+from _pytest.compat import overload
 from _pytest.compat import TYPE_CHECKING
 from _pytest.config import Config
 from _pytest.config import directory_arg
 from _pytest.config import ExitCode
 from _pytest.config import hookimpl
 from _pytest.config import UsageError
+from _pytest.config.argparsing import Parser
 from _pytest.fixtures import FixtureManager
 from _pytest.outcomes import exit
 from _pytest.reports import CollectReport
@@ -38,7 +42,7 @@ if TYPE_CHECKING:
     from _pytest.python import Package
 
 
-def pytest_addoption(parser):
+def pytest_addoption(parser: Parser) -> None:
     parser.addini(
         "norecursedirs",
         "directory patterns to avoid for recursion",
@@ -241,7 +245,7 @@ def wrap_session(
     return session.exitstatus
 
 
-def pytest_cmdline_main(config):
+def pytest_cmdline_main(config: Config) -> Union[int, ExitCode]:
     return wrap_session(config, _main)
 
 
@@ -258,11 +262,11 @@ def _main(config: Config, session: "Session") -> Optional[Union[int, ExitCode]]:
     return None
 
 
-def pytest_collection(session):
+def pytest_collection(session: "Session") -> Sequence[nodes.Item]:
     return session.perform_collect()
 
 
-def pytest_runtestloop(session):
+def pytest_runtestloop(session: "Session") -> bool:
     if session.testsfailed and not session.config.option.continue_on_collection_errors:
         raise session.Interrupted(
             "%d error%s during collection"
@@ -282,7 +286,7 @@ def pytest_runtestloop(session):
     return True
 
 
-def _in_venv(path):
+def _in_venv(path: py.path.local) -> bool:
     """Attempts to detect if ``path`` is the root of a Virtual Environment by
     checking for the existence of the appropriate activate script"""
     bindir = path.join("Scripts" if sys.platform.startswith("win") else "bin")
@@ -328,7 +332,7 @@ def pytest_ignore_collect(
     return None
 
 
-def pytest_collection_modifyitems(items, config):
+def pytest_collection_modifyitems(items, config: Config) -> None:
     deselect_prefixes = tuple(config.getoption("deselect") or [])
     if not deselect_prefixes:
         return
@@ -385,8 +389,8 @@ class Session(nodes.FSCollector):
         )
         self.testsfailed = 0
         self.testscollected = 0
-        self.shouldstop = False
-        self.shouldfail = False
+        self.shouldstop = False  # type: Union[bool, str]
+        self.shouldfail = False  # type: Union[bool, str]
         self.trace = config.trace.root.get("collection")
         self.startdir = config.invocation_dir
         self._initialpaths = frozenset()  # type: FrozenSet[py.path.local]
@@ -412,10 +416,11 @@ class Session(nodes.FSCollector):
         self.config.pluginmanager.register(self, name="session")
 
     @classmethod
-    def from_config(cls, config):
-        return cls._create(config)
+    def from_config(cls, config: Config) -> "Session":
+        session = cls._create(config)  # type: Session
+        return session
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return "<%s %s exitstatus=%r testsfailed=%d testscollected=%d>" % (
             self.__class__.__name__,
             self.name,
@@ -429,14 +434,14 @@ class Session(nodes.FSCollector):
         return self._bestrelpathcache[node_path]
 
     @hookimpl(tryfirst=True)
-    def pytest_collectstart(self):
+    def pytest_collectstart(self) -> None:
         if self.shouldfail:
             raise self.Failed(self.shouldfail)
         if self.shouldstop:
             raise self.Interrupted(self.shouldstop)
 
     @hookimpl(tryfirst=True)
-    def pytest_runtest_logreport(self, report):
+    def pytest_runtest_logreport(self, report) -> None:
         if report.failed and not hasattr(report, "wasxfail"):
             self.testsfailed += 1
             maxfail = self.config.getvalue("maxfail")
@@ -445,13 +450,27 @@ class Session(nodes.FSCollector):
 
     pytest_collectreport = pytest_runtest_logreport
 
-    def isinitpath(self, path):
+    def isinitpath(self, path: py.path.local) -> bool:
         return path in self._initialpaths
 
     def gethookproxy(self, fspath: py.path.local):
         return super()._gethookproxy(fspath)
 
-    def perform_collect(self, args=None, genitems=True):
+    @overload
+    def perform_collect(
+        self, args: Optional[Sequence[str]] = ..., genitems: "Literal[True]" = ...
+    ) -> Sequence[nodes.Item]:
+        raise NotImplementedError()
+
+    @overload  # noqa: F811
+    def perform_collect(  # noqa: F811
+        self, args: Optional[Sequence[str]] = ..., genitems: bool = ...
+    ) -> Sequence[Union[nodes.Item, nodes.Collector]]:
+        raise NotImplementedError()
+
+    def perform_collect(  # noqa: F811
+        self, args: Optional[Sequence[str]] = None, genitems: bool = True
+    ) -> Sequence[Union[nodes.Item, nodes.Collector]]:
         hook = self.config.hook
         try:
             items = self._perform_collect(args, genitems)
@@ -464,15 +483,29 @@ class Session(nodes.FSCollector):
         self.testscollected = len(items)
         return items
 
-    def _perform_collect(self, args, genitems):
+    @overload
+    def _perform_collect(
+        self, args: Optional[Sequence[str]], genitems: "Literal[True]"
+    ) -> Sequence[nodes.Item]:
+        raise NotImplementedError()
+
+    @overload  # noqa: F811
+    def _perform_collect(  # noqa: F811
+        self, args: Optional[Sequence[str]], genitems: bool
+    ) -> Sequence[Union[nodes.Item, nodes.Collector]]:
+        raise NotImplementedError()
+
+    def _perform_collect(  # noqa: F811
+        self, args: Optional[Sequence[str]], genitems: bool
+    ) -> Sequence[Union[nodes.Item, nodes.Collector]]:
         if args is None:
             args = self.config.args
         self.trace("perform_collect", self, args)
         self.trace.root.indent += 1
-        self._notfound = []
+        self._notfound = []  # type: List[Tuple[str, NoMatch]]
         initialpaths = []  # type: List[py.path.local]
         self._initial_parts = []  # type: List[Tuple[py.path.local, List[str]]]
-        self.items = items = []
+        self.items = items = []  # type: List[nodes.Item]
         for arg in args:
             fspath, parts = self._parsearg(arg)
             self._initial_parts.append((fspath, parts))
@@ -495,7 +528,7 @@ class Session(nodes.FSCollector):
                     self.items.extend(self.genitems(node))
             return items
 
-    def collect(self):
+    def collect(self) -> Iterator[Union[nodes.Item, nodes.Collector]]:
         for fspath, parts in self._initial_parts:
             self.trace("processing argument", (fspath, parts))
             self.trace.root.indent += 1
@@ -513,7 +546,9 @@ class Session(nodes.FSCollector):
         self._collection_node_cache3.clear()
         self._collection_pkg_roots.clear()
 
-    def _collect(self, argpath, names):
+    def _collect(
+        self, argpath: py.path.local, names: List[str]
+    ) -> Iterator[Union[nodes.Item, nodes.Collector]]:
         from _pytest.python import Package
 
         # Start with a Session root, and delve to argpath item (dir or file)
@@ -541,7 +576,7 @@ class Session(nodes.FSCollector):
         if argpath.check(dir=1):
             assert not names, "invalid arg {!r}".format((argpath, names))
 
-            seen_dirs = set()
+            seen_dirs = set()  # type: Set[py.path.local]
             for path in argpath.visit(
                 fil=self._visit_filter, rec=self._recurse, bf=True, sort=True
             ):
@@ -582,8 +617,9 @@ class Session(nodes.FSCollector):
             # Module itself, so just use that. If this special case isn't taken, then all
             # the files in the package will be yielded.
             if argpath.basename == "__init__.py":
+                assert isinstance(m[0], nodes.Collector)
                 try:
-                    yield next(m[0].collect())
+                    yield next(iter(m[0].collect()))
                 except StopIteration:
                     # The package collects nothing with only an __init__.py
                     # file in it, which gets ignored by the default
@@ -593,10 +629,11 @@ class Session(nodes.FSCollector):
             yield from m
 
     @staticmethod
-    def _visit_filter(f):
-        return f.check(file=1)
+    def _visit_filter(f: py.path.local) -> bool:
+        # TODO: Remove type: ignore once `py` is typed.
+        return f.check(file=1)  # type: ignore
 
-    def _tryconvertpyarg(self, x):
+    def _tryconvertpyarg(self, x: str) -> str:
         """Convert a dotted module name to path."""
         try:
             spec = importlib.util.find_spec(x)
@@ -605,14 +642,14 @@ class Session(nodes.FSCollector):
         # ValueError: not a module name
         except (AttributeError, ImportError, ValueError):
             return x
-        if spec is None or spec.origin in {None, "namespace"}:
+        if spec is None or spec.origin is None or spec.origin == "namespace":
             return x
         elif spec.submodule_search_locations:
             return os.path.dirname(spec.origin)
         else:
             return spec.origin
 
-    def _parsearg(self, arg):
+    def _parsearg(self, arg: str) -> Tuple[py.path.local, List[str]]:
         """ return (fspath, names) tuple after checking the file exists. """
         strpath, *parts = str(arg).split("::")
         if self.config.option.pyargs:
@@ -628,7 +665,9 @@ class Session(nodes.FSCollector):
         fspath = fspath.realpath()
         return (fspath, parts)
 
-    def matchnodes(self, matching, names):
+    def matchnodes(
+        self, matching: Sequence[Union[nodes.Item, nodes.Collector]], names: List[str],
+    ) -> Sequence[Union[nodes.Item, nodes.Collector]]:
         self.trace("matchnodes", matching, names)
         self.trace.root.indent += 1
         nodes = self._matchnodes(matching, names)
@@ -639,13 +678,15 @@ class Session(nodes.FSCollector):
             raise NoMatch(matching, names[:1])
         return nodes
 
-    def _matchnodes(self, matching, names):
+    def _matchnodes(
+        self, matching: Sequence[Union[nodes.Item, nodes.Collector]], names: List[str],
+    ) -> Sequence[Union[nodes.Item, nodes.Collector]]:
         if not matching or not names:
             return matching
         name = names[0]
         assert name
         nextnames = names[1:]
-        resultnodes = []
+        resultnodes = []  # type: List[Union[nodes.Item, nodes.Collector]]
         for node in matching:
             if isinstance(node, nodes.Item):
                 if not names:
@@ -676,7 +717,9 @@ class Session(nodes.FSCollector):
                 node.ihook.pytest_collectreport(report=rep)
         return resultnodes
 
-    def genitems(self, node):
+    def genitems(
+        self, node: Union[nodes.Item, nodes.Collector]
+    ) -> Iterator[nodes.Item]:
         self.trace("genitems", node)
         if isinstance(node, nodes.Item):
             node.ihook.pytest_itemcollected(item=node)
diff --git a/src/_pytest/nodes.py b/src/_pytest/nodes.py
index c9b633579..010dce925 100644
--- a/src/_pytest/nodes.py
+++ b/src/_pytest/nodes.py
@@ -4,8 +4,10 @@ from functools import lru_cache
 from typing import Any
 from typing import Callable
 from typing import Dict
+from typing import Iterable
 from typing import List
 from typing import Optional
+from typing import Sequence
 from typing import Set
 from typing import Tuple
 from typing import Union
@@ -226,7 +228,7 @@ class Node(metaclass=NodeMeta):
 
     # methods for ordering nodes
     @property
-    def nodeid(self):
+    def nodeid(self) -> str:
         """ a ::-separated string denoting its collection tree address. """
         return self._nodeid
 
@@ -423,7 +425,7 @@ class Collector(Node):
     class CollectError(Exception):
         """ an error during collection, contains a custom message. """
 
-    def collect(self):
+    def collect(self) -> Iterable[Union["Item", "Collector"]]:
         """ returns a list of children (items and collectors)
             for this collection node.
         """
@@ -522,6 +524,9 @@ class FSCollector(Collector):
             proxy = self.config.hook
         return proxy
 
+    def gethookproxy(self, fspath: py.path.local):
+        raise NotImplementedError()
+
     def _recurse(self, dirpath: py.path.local) -> bool:
         if dirpath.basename == "__pycache__":
             return False
@@ -535,7 +540,12 @@ class FSCollector(Collector):
         ihook.pytest_collect_directory(path=dirpath, parent=self)
         return True
 
-    def _collectfile(self, path, handle_dupes=True):
+    def isinitpath(self, path: py.path.local) -> bool:
+        raise NotImplementedError()
+
+    def _collectfile(
+        self, path: py.path.local, handle_dupes: bool = True
+    ) -> Sequence[Collector]:
         assert (
             path.isfile()
         ), "{!r} is not a file (isdir={!r}, exists={!r}, islink={!r})".format(
@@ -555,7 +565,7 @@ class FSCollector(Collector):
                 else:
                     duplicate_paths.add(path)
 
-        return ihook.pytest_collect_file(path=path, parent=self)
+        return ihook.pytest_collect_file(path=path, parent=self)  # type: ignore[no-any-return] # noqa: F723
 
 
 class File(FSCollector):
diff --git a/src/_pytest/python.py b/src/_pytest/python.py
index e46d498ab..e05aa398d 100644
--- a/src/_pytest/python.py
+++ b/src/_pytest/python.py
@@ -43,9 +43,9 @@ from _pytest.compat import REGEX_TYPE
 from _pytest.compat import safe_getattr
 from _pytest.compat import safe_isclass
 from _pytest.compat import STRING_TYPES
+from _pytest.compat import TYPE_CHECKING
 from _pytest.config import Config
 from _pytest.config import ExitCode
-from _pytest.compat import TYPE_CHECKING
 from _pytest.config import hookimpl
 from _pytest.config.argparsing import Parser
 from _pytest.deprecated import FUNCARGNAMES
@@ -184,16 +184,20 @@ def pytest_pyfunc_call(pyfuncitem: "Function"):
     return True
 
 
-def pytest_collect_file(path, parent):
+def pytest_collect_file(path: py.path.local, parent) -> Optional["Module"]:
     ext = path.ext
     if ext == ".py":
         if not parent.session.isinitpath(path):
             if not path_matches_patterns(
                 path, parent.config.getini("python_files") + ["__init__.py"]
             ):
-                return
+                return None
         ihook = parent.session.gethookproxy(path)
-        return ihook.pytest_pycollect_makemodule(path=path, parent=parent)
+        module = ihook.pytest_pycollect_makemodule(
+            path=path, parent=parent
+        )  # type: Module
+        return module
+    return None
 
 
 def path_matches_patterns(path, patterns):
@@ -201,14 +205,16 @@ def path_matches_patterns(path, patterns):
     return any(path.fnmatch(pattern) for pattern in patterns)
 
 
-def pytest_pycollect_makemodule(path, parent):
+def pytest_pycollect_makemodule(path: py.path.local, parent) -> "Module":
     if path.basename == "__init__.py":
-        return Package.from_parent(parent, fspath=path)
-    return Module.from_parent(parent, fspath=path)
+        pkg = Package.from_parent(parent, fspath=path)  # type: Package
+        return pkg
+    mod = Module.from_parent(parent, fspath=path)  # type: Module
+    return mod
 
 
 @hookimpl(hookwrapper=True)
-def pytest_pycollect_makeitem(collector, name, obj):
+def pytest_pycollect_makeitem(collector: "PyCollector", name: str, obj):
     outcome = yield
     res = outcome.get_result()
     if res is not None:
@@ -372,7 +378,7 @@ class PyCollector(PyobjMixin, nodes.Collector):
                 return True
         return False
 
-    def collect(self):
+    def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         if not getattr(self.obj, "__test__", True):
             return []
 
@@ -381,8 +387,8 @@ class PyCollector(PyobjMixin, nodes.Collector):
         dicts = [getattr(self.obj, "__dict__", {})]
         for basecls in self.obj.__class__.__mro__:
             dicts.append(basecls.__dict__)
-        seen = set()
-        values = []
+        seen = set()  # type: Set[str]
+        values = []  # type: List[Union[nodes.Item, nodes.Collector]]
         for dic in dicts:
             # Note: seems like the dict can change during iteration -
             # be careful not to remove the list() without consideration.
@@ -404,9 +410,16 @@ class PyCollector(PyobjMixin, nodes.Collector):
         values.sort(key=sort_key)
         return values
 
-    def _makeitem(self, name, obj):
+    def _makeitem(
+        self, name: str, obj
+    ) -> Union[
+        None, nodes.Item, nodes.Collector, List[Union[nodes.Item, nodes.Collector]]
+    ]:
         # assert self.ihook.fspath == self.fspath, self
-        return self.ihook.pytest_pycollect_makeitem(collector=self, name=name, obj=obj)
+        item = self.ihook.pytest_pycollect_makeitem(
+            collector=self, name=name, obj=obj
+        )  # type: Union[None, nodes.Item, nodes.Collector, List[Union[nodes.Item, nodes.Collector]]]
+        return item
 
     def _genfunctions(self, name, funcobj):
         module = self.getparent(Module).obj
@@ -458,7 +471,7 @@ class Module(nodes.File, PyCollector):
     def _getobj(self):
         return self._importtestmodule()
 
-    def collect(self):
+    def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         self._inject_setup_module_fixture()
         self._inject_setup_function_fixture()
         self.session._fixturemanager.parsefactories(self)
@@ -603,17 +616,17 @@ class Package(Module):
     def gethookproxy(self, fspath: py.path.local):
         return super()._gethookproxy(fspath)
 
-    def isinitpath(self, path):
+    def isinitpath(self, path: py.path.local) -> bool:
         return path in self.session._initialpaths
 
-    def collect(self):
+    def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         this_path = self.fspath.dirpath()
         init_module = this_path.join("__init__.py")
         if init_module.check(file=1) and path_matches_patterns(
             init_module, self.config.getini("python_files")
         ):
             yield Module.from_parent(self, fspath=init_module)
-        pkg_prefixes = set()
+        pkg_prefixes = set()  # type: Set[py.path.local]
         for path in this_path.visit(rec=self._recurse, bf=True, sort=True):
             # We will visit our own __init__.py file, in which case we skip it.
             is_file = path.isfile()
@@ -670,10 +683,11 @@ class Class(PyCollector):
         """
         return super().from_parent(name=name, parent=parent)
 
-    def collect(self):
+    def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         if not safe_getattr(self.obj, "__test__", True):
             return []
         if hasinit(self.obj):
+            assert self.parent is not None
             self.warn(
                 PytestCollectionWarning(
                     "cannot collect test class %r because it has a "
@@ -683,6 +697,7 @@ class Class(PyCollector):
             )
             return []
         elif hasnew(self.obj):
+            assert self.parent is not None
             self.warn(
                 PytestCollectionWarning(
                     "cannot collect test class %r because it has a "
@@ -756,7 +771,7 @@ class Instance(PyCollector):
     def _getobj(self):
         return self.parent.obj()
 
-    def collect(self):
+    def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         self.session._fixturemanager.parsefactories(self)
         return super().collect()
 
diff --git a/src/_pytest/reports.py b/src/_pytest/reports.py
index 178df6004..908ba7d3b 100644
--- a/src/_pytest/reports.py
+++ b/src/_pytest/reports.py
@@ -21,7 +21,8 @@ from _pytest._code.code import ReprTraceback
 from _pytest._code.code import TerminalRepr
 from _pytest._io import TerminalWriter
 from _pytest.compat import TYPE_CHECKING
-from _pytest.nodes import Node
+from _pytest.nodes import Collector
+from _pytest.nodes import Item
 from _pytest.outcomes import skip
 from _pytest.pathlib import Path
 
@@ -316,7 +317,13 @@ class CollectReport(BaseReport):
     when = "collect"
 
     def __init__(
-        self, nodeid: str, outcome, longrepr, result: List[Node], sections=(), **extra
+        self,
+        nodeid: str,
+        outcome,
+        longrepr,
+        result: Optional[List[Union[Item, Collector]]],
+        sections=(),
+        **extra
     ) -> None:
         self.nodeid = nodeid
         self.outcome = outcome
diff --git a/src/_pytest/runner.py b/src/_pytest/runner.py
index c7f6d8811..a2b9ee207 100644
--- a/src/_pytest/runner.py
+++ b/src/_pytest/runner.py
@@ -404,10 +404,10 @@ class SetupState:
                 raise e
 
 
-def collect_one_node(collector):
+def collect_one_node(collector: Collector) -> CollectReport:
     ihook = collector.ihook
     ihook.pytest_collectstart(collector=collector)
-    rep = ihook.pytest_make_collect_report(collector=collector)
+    rep = ihook.pytest_make_collect_report(collector=collector)  # type: CollectReport
     call = rep.__dict__.pop("call", None)
     if call and check_interactive_exception(call, rep):
         ihook.pytest_exception_interact(node=collector, call=call, report=rep)
diff --git a/src/_pytest/unittest.py b/src/_pytest/unittest.py
index 0d9133f60..b2e6ab89d 100644
--- a/src/_pytest/unittest.py
+++ b/src/_pytest/unittest.py
@@ -1,32 +1,43 @@
 """ discovery and running of std-library "unittest" style tests. """
 import sys
 import traceback
+from typing import Iterable
+from typing import Optional
+from typing import Union
 
 import _pytest._code
 import pytest
 from _pytest.compat import getimfunc
 from _pytest.compat import is_async_function
 from _pytest.config import hookimpl
+from _pytest.nodes import Collector
+from _pytest.nodes import Item
 from _pytest.outcomes import exit
 from _pytest.outcomes import fail
 from _pytest.outcomes import skip
 from _pytest.outcomes import xfail
 from _pytest.python import Class
 from _pytest.python import Function
+from _pytest.python import PyCollector
 from _pytest.runner import CallInfo
 from _pytest.skipping import skipped_by_mark_key
 from _pytest.skipping import unexpectedsuccess_key
 
 
-def pytest_pycollect_makeitem(collector, name, obj):
+def pytest_pycollect_makeitem(
+    collector: PyCollector, name: str, obj
+) -> Optional["UnitTestCase"]:
     # has unittest been imported and is obj a subclass of its TestCase?
     try:
-        if not issubclass(obj, sys.modules["unittest"].TestCase):
-            return
+        ut = sys.modules["unittest"]
+        # Type ignored because `ut` is an opaque module.
+        if not issubclass(obj, ut.TestCase):  # type: ignore
+            return None
     except Exception:
-        return
+        return None
     # yes, so let's collect it
-    return UnitTestCase.from_parent(collector, name=name, obj=obj)
+    item = UnitTestCase.from_parent(collector, name=name, obj=obj)  # type: UnitTestCase
+    return item
 
 
 class UnitTestCase(Class):
@@ -34,7 +45,7 @@ class UnitTestCase(Class):
     # to declare that our children do not support funcargs
     nofuncargs = True
 
-    def collect(self):
+    def collect(self) -> Iterable[Union[Item, Collector]]:
         from unittest import TestLoader
 
         cls = self.obj
@@ -61,8 +72,8 @@ class UnitTestCase(Class):
             runtest = getattr(self.obj, "runTest", None)
             if runtest is not None:
                 ut = sys.modules.get("twisted.trial.unittest", None)
-                if ut is None or runtest != ut.TestCase.runTest:
-                    # TODO: callobj consistency
+                # Type ignored because `ut` is an opaque module.
+                if ut is None or runtest != ut.TestCase.runTest:  # type: ignore
                     yield TestCaseFunction.from_parent(self, name="runTest")
 
     def _inject_setup_teardown_fixtures(self, cls):