diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 45aa4d9a824..45710a70177 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -796,7 +796,7 @@ def __init__(self, pluginmanager, *, invocation_params=None) -> None:
         )
 
     @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 0140e0b3a98..d0ee40ad865 100644
--- a/src/_pytest/doctest.py
+++ b/src/_pytest/doctest.py
@@ -7,6 +7,7 @@
 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
@@ -108,13 +109,18 @@ def pytest_unconfigure():
     RUNNER_CLASS = None
 
 
-def pytest_collect_file(path, 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(config, path, parent):
-            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(config, path, parent):
@@ -361,7 +367,7 @@ 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,
@@ -440,7 +446,7 @@ def _mock_aware_unwrap(obj, stop=None):
 
 
 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 3cd7f5ffebb..9bf59b52ef9 100644
--- a/src/_pytest/hookspec.py
+++ b/src/_pytest/hookspec.py
@@ -1,13 +1,20 @@
 """ hook specifications for pytest plugins, invoked from main.py and builtin plugins.  """
 from typing import Any
+from typing import List
 from typing import Optional
+from typing import Union
 
+import py.path
 from pluggy import HookspecMarker
 
 from _pytest.compat import TYPE_CHECKING
 
 if TYPE_CHECKING:
     from _pytest.main import Session
+    from _pytest.nodes import Collector
+    from _pytest.nodes import Item
+    from _pytest.python import Module
+    from _pytest.python import PyCollector
 
 
 hookspec = HookspecMarker("pytest")
@@ -215,7 +222,7 @@ 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.
 
@@ -255,7 +262,7 @@ 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
@@ -268,7 +275,9 @@ 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 dbb6236a3ec..9961a2c69bb 100644
--- a/src/_pytest/main.py
+++ b/src/_pytest/main.py
@@ -5,11 +5,14 @@
 import os
 import sys
 from typing import Callable
+from typing import cast
 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 +21,14 @@
 
 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
@@ -33,11 +38,12 @@
 
 if TYPE_CHECKING:
     from typing import Type
+    from typing_extensions import Literal
 
     from _pytest.python import Package
 
 
-def pytest_addoption(parser):
+def pytest_addoption(parser: Parser) -> None:
     parser.addini(
         "norecursedirs",
         "directory patterns to avoid for recursion",
@@ -237,7 +243,7 @@ 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)
 
 
@@ -254,11 +260,11 @@ 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"
@@ -278,7 +284,7 @@ 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")
@@ -295,7 +301,7 @@ def _in_venv(path):
     return any([fname.basename in activates for fname in bindir.listdir()])
 
 
-def pytest_ignore_collect(path, config):
+def pytest_ignore_collect(path: py.path.local, config: Config) -> bool:
     ignore_paths = config._getconftest_pathlist("collect_ignore", path=path.dirpath())
     ignore_paths = ignore_paths or []
     excludeopt = config.getoption("ignore")
@@ -323,7 +329,7 @@ def pytest_ignore_collect(path, config):
     return False
 
 
-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
@@ -380,8 +386,8 @@ def __init__(self, config: Config) -> None:
         )
         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]
@@ -407,10 +413,11 @@ def __init__(self, config: Config) -> None:
         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,
@@ -424,14 +431,14 @@ def _node_location_to_relpath(self, node_path: py.path.local) -> str:
         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")
@@ -440,13 +447,27 @@ def pytest_runtest_logreport(self, report):
 
     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)
@@ -459,15 +480,29 @@ def perform_collect(self, args=None, genitems=True):
         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))
@@ -490,7 +525,7 @@ def _perform_collect(self, args, genitems):
                     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
@@ -500,7 +535,8 @@ def collect(self):
                 report_arg = "::".join((str(fspath), *parts))
                 # we are inside a make_report hook so
                 # we cannot directly pass through the exception
-                self._notfound.append((report_arg, sys.exc_info()[1]))
+                exc = cast(NoMatch, sys.exc_info()[1])
+                self._notfound.append((report_arg, exc))
 
             self.trace.root.indent -= 1
         self._collection_node_cache1.clear()
@@ -508,7 +544,9 @@ def collect(self):
         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)
@@ -536,7 +574,7 @@ def _collect(self, argpath, names):
         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
             ):
@@ -577,8 +615,9 @@ def _collect(self, argpath, names):
             # 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
@@ -587,7 +626,9 @@ def _collect(self, argpath, names):
                 return
             yield from m
 
-    def _collectfile(self, path, handle_dupes=True):
+    def _collectfile(
+        self, path: py.path.local, handle_dupes: bool = True
+    ) -> Sequence[nodes.Collector]:
         assert (
             path.isfile()
         ), "{!r} is not a file (isdir={!r}, exists={!r}, islink={!r})".format(
@@ -607,13 +648,17 @@ def _collectfile(self, path, handle_dupes=True):
                 else:
                     duplicate_paths.add(path)
 
-        return ihook.pytest_collect_file(path=path, parent=self)
+        collector = ihook.pytest_collect_file(
+            path=path, parent=self
+        )  # type: List[nodes.Collector]
+        return collector
 
     @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)
@@ -622,14 +667,14 @@ def _tryconvertpyarg(self, x):
         # 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:
@@ -645,7 +690,9 @@ def _parsearg(self, arg):
         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)
@@ -656,13 +703,15 @@ def matchnodes(self, matching, names):
             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:
@@ -693,7 +742,9 @@ def _matchnodes(self, matching, names):
                 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 81a25ddd5c2..99453941124 100644
--- a/src/_pytest/nodes.py
+++ b/src/_pytest/nodes.py
@@ -3,6 +3,7 @@
 from functools import lru_cache
 from typing import Any
 from typing import Dict
+from typing import Iterable
 from typing import List
 from typing import Optional
 from typing import Set
@@ -205,7 +206,7 @@ def warn(self, warning):
 
     # methods for ordering nodes
     @property
-    def nodeid(self):
+    def nodeid(self) -> str:
         """ a ::-separated string denoting its collection tree address. """
         return self._nodeid
 
@@ -390,7 +391,7 @@ 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.
         """
diff --git a/src/_pytest/python.py b/src/_pytest/python.py
index 6402164f9e4..a9264667119 100644
--- a/src/_pytest/python.py
+++ b/src/_pytest/python.py
@@ -4,14 +4,17 @@
 import inspect
 import os
 import sys
+import typing
 import warnings
 from collections import Counter
 from collections import defaultdict
 from collections.abc import Sequence
 from functools import partial
 from typing import Dict
+from typing import Iterable
 from typing import List
 from typing import Optional
+from typing import Set
 from typing import Tuple
 from typing import Union
 
@@ -177,16 +180,20 @@ 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):
@@ -194,14 +201,16 @@ 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:
@@ -353,7 +362,7 @@ def _matches_prefix_or_glob_option(self, option_name, name):
                 return True
         return False
 
-    def collect(self):
+    def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         if not getattr(self.obj, "__test__", True):
             return []
 
@@ -362,8 +371,8 @@ def collect(self):
         dicts = [getattr(self.obj, "__dict__", {})]
         for basecls in inspect.getmro(self.obj.__class__):
             dicts.append(basecls.__dict__)
-        seen = {}
-        values = []
+        seen = {}  # type: Dict[str, bool]
+        values = []  # type: List[Union[nodes.Item, nodes.Collector]]
         for dic in dicts:
             for name, obj in list(dic.items()):
                 if name in seen:
@@ -383,9 +392,16 @@ def sort_key(item):
         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
@@ -437,7 +453,7 @@ 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)
@@ -584,7 +600,9 @@ def setup(self):
     def gethookproxy(self, fspath: py.path.local):
         return super()._gethookproxy(fspath)
 
-    def _collectfile(self, path, handle_dupes=True):
+    def _collectfile(
+        self, path: py.path.local, handle_dupes: bool = True
+    ) -> typing.Sequence[nodes.Collector]:
         assert (
             path.isfile()
         ), "{!r} is not a file (isdir={!r}, exists={!r}, islink={!r})".format(
@@ -607,19 +625,22 @@ def _collectfile(self, path, handle_dupes=True):
         if self.fspath == path:  # __init__.py
             return [self]
 
-        return ihook.pytest_collect_file(path=path, parent=self)
+        collectors = ihook.pytest_collect_file(
+            path=path, parent=self
+        )  # type: List[nodes.Collector]
+        return collectors
 
-    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()
@@ -676,10 +697,11 @@ def from_parent(cls, parent, *, name, obj=None):
         """
         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 "
@@ -689,6 +711,7 @@ def collect(self):
             )
             return []
         elif hasnew(self.obj):
+            assert self.parent is not None
             self.warn(
                 PytestCollectionWarning(
                     "cannot collect test class %r because it has a "
@@ -762,7 +785,7 @@ 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 3ad67c224c4..d3bfc91979a 100644
--- a/src/_pytest/reports.py
+++ b/src/_pytest/reports.py
@@ -20,7 +20,8 @@
 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
 
@@ -315,7 +316,13 @@ 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 e10e4d8bdf0..3eb9ca28667 100644
--- a/src/_pytest/runner.py
+++ b/src/_pytest/runner.py
@@ -373,10 +373,10 @@ def prepare(self, colitem):
                 raise
 
 
-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 a5512e9443c..3740ff1249a 100644
--- a/src/_pytest/unittest.py
+++ b/src/_pytest/unittest.py
@@ -2,29 +2,40 @@
 import functools
 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.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
 
 
-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):
@@ -32,7 +43,7 @@ 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
@@ -59,8 +70,8 @@ def collect(self):
             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):