diff --git a/src/_pytest/_io/__init__.py b/src/_pytest/_io/__init__.py
index f52505c0291..928d72a638b 100644
--- a/src/_pytest/_io/__init__.py
+++ b/src/_pytest/_io/__init__.py
@@ -1,10 +1,71 @@
+import os
+import sys
 from typing import List
 from typing import Sequence
 
 import py.io
 
+from _pytest.compat import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from typing import TextIO
+
+
+def use_markup(file: "TextIO") -> bool:
+    # Backward compatibility with pylib: handle PY_COLORS={0,1} only.
+    val = os.getenv("PY_COLORS")
+    if val in ("0", "1"):
+        return val == "1"
+
+    # TODO
+    # # PYTEST_FORCE_COLOR: handled as boolean.
+    # val = os.getenv("PYTEST_FORCE_COLOR")
+    # if val is not None:
+    #     from _pytest.config import _strtobool
+    #
+    #     return _strtobool(val)
+
+    # NO_COLOR: disable markup with any value (https://no-color.org/).
+    if "NO_COLOR" in os.environ:
+        return False
+
+    # TODO
+    # if _running_on_ci():
+    #     return True
+
+    return file.isatty() if hasattr(file, "isatty") else False
+
 
 class TerminalWriter(py.io.TerminalWriter):  # noqa: pygrep-py
+    def __init__(self, file: "TextIO" = None) -> None:
+        if file is None:
+            file = sys.stdout
+        if hasattr(file, "isatty") and file.isatty() and sys.platform == "win32":
+            try:
+                import colorama
+            except ImportError:
+                pass
+            else:
+                file = colorama.AnsiToWin32(file).stream
+                assert file is not None
+        self._file = file
+        self._lastlen = 0
+        self._chars_on_current_line = 0
+        self._width_of_current_line = 0
+        self.hasmarkup = use_markup(self._file)
+
+    def write(self, msg: str, **markup: bool) -> int:  # type: ignore[override]
+        if not msg:
+            return 0
+        self._update_chars_on_current_line(msg)  # type: ignore[attr-defined]
+        if self.hasmarkup and markup:
+            markupmsg = self.markup(msg, **markup)
+        else:
+            markupmsg = msg
+        ret = self._file.write(markupmsg)
+        self._file.flush()
+        return ret
+
     @property
     def fullwidth(self):
         if hasattr(self, "_terminal_width"):
@@ -50,3 +111,7 @@ def _highlight(self, source):
             return source
         else:
             return highlight(source, PythonLexer(), TerminalFormatter(bg="dark"))
+
+
+def _running_on_ci():
+    return os.environ.get("CI", "").lower() == "true" or "BUILD_NUMBER" in os.environ
diff --git a/src/_pytest/assertion/truncate.py b/src/_pytest/assertion/truncate.py
index 9b294bc18dd..b4c9fc37013 100644
--- a/src/_pytest/assertion/truncate.py
+++ b/src/_pytest/assertion/truncate.py
@@ -5,7 +5,6 @@
 ~8 terminal lines, unless running in "-vv" mode or running on CI.
 """
 from ..compat import TYPE_CHECKING
-from _pytest.assertion.util import _running_on_ci
 
 if TYPE_CHECKING:
     from typing import List
@@ -28,7 +27,12 @@ def _should_truncate(config: "Config") -> bool:
     level = config.getini("assert_truncate_level")  # type: str
     verbose = config.option.verbose  # type: int
     if level == "auto":
-        return verbose < 2 and not _running_on_ci()
+        if verbose >= 2:
+            return False
+
+        from _pytest._io import _running_on_ci
+
+        return not _running_on_ci()
     return int(level) > verbose
 
 
diff --git a/src/_pytest/assertion/util.py b/src/_pytest/assertion/util.py
index 756df116268..7bb4c54194d 100644
--- a/src/_pytest/assertion/util.py
+++ b/src/_pytest/assertion/util.py
@@ -1,7 +1,6 @@
 """Utilities for assertion debugging"""
 import collections.abc
 import itertools
-import os
 import pprint
 import re
 from typing import AbstractSet
@@ -534,7 +533,3 @@ def _notin_text(term: str, text: str, verbose: int = 0) -> List[str]:
         "? " + indent + marker,
     ]
     return newdiff
-
-
-def _running_on_ci():
-    return os.environ.get("CI", "").lower() == "true" or "BUILD_NUMBER" in os.environ
diff --git a/src/_pytest/pastebin.py b/src/_pytest/pastebin.py
index b9df21c5ebf..05adcc8a8fd 100644
--- a/src/_pytest/pastebin.py
+++ b/src/_pytest/pastebin.py
@@ -1,5 +1,6 @@
 """ submit failure or test session information to a pastebin service. """
 import tempfile
+from io import StringIO
 
 import pytest
 
@@ -93,11 +94,10 @@ def pytest_terminal_summary(terminalreporter):
                 msg = rep.longrepr.reprtraceback.reprentries[-1].reprfileloc
             except AttributeError:
                 msg = tr._getfailureheadline(rep)
-            tw = _pytest.config.create_terminal_writer(
-                terminalreporter.config, stringio=True
-            )
+            file = StringIO()
+            tw = _pytest.config.create_terminal_writer(tr.config, file=file)
             rep.toterminal(tw)
-            s = tw.stringio.getvalue()
+            s = file.getvalue()
             assert len(s)
             pastebinurl = create_new_paste(s)
             tr.write_line("{} --> {}".format(msg, pastebinurl))
diff --git a/src/_pytest/reports.py b/src/_pytest/reports.py
index 0db5b57b240..e8533dd0605 100644
--- a/src/_pytest/reports.py
+++ b/src/_pytest/reports.py
@@ -75,17 +75,18 @@ def get_sections(self, prefix):
                 yield prefix, content
 
     @property
-    def longreprtext(self):
+    def longreprtext(self) -> str:
         """
         Read-only property that returns the full string representation
         of ``longrepr``.
 
         .. versionadded:: 3.0
         """
-        tw = TerminalWriter(stringio=True)
+        file = StringIO()
+        tw = TerminalWriter(file)
         tw.hasmarkup = False
         self.toterminal(tw)
-        exc = tw.stringio.getvalue()
+        exc = file.getvalue()
         return exc.strip()
 
     @property
diff --git a/src/_pytest/terminal.py b/src/_pytest/terminal.py
index ad96787be22..3fc00c6c875 100644
--- a/src/_pytest/terminal.py
+++ b/src/_pytest/terminal.py
@@ -34,7 +34,6 @@
 from _pytest import nodes
 from _pytest._code.code import ExceptionInfo
 from _pytest._code.code import ReprFileLocation
-from _pytest.assertion.util import _running_on_ci
 from _pytest.compat import order_preserving_dict
 from _pytest.compat import shell_quote
 from _pytest.compat import TYPE_CHECKING
@@ -1214,10 +1213,15 @@ def short_test_summary(self) -> None:
         if not self.reportchars:
             return
 
-        if not self.isatty or _running_on_ci():
+        if not self.isatty:
             termwidth = None
         else:
-            termwidth = self._tw.fullwidth
+            from _pytest._io import _running_on_ci
+
+            if _running_on_ci():
+                termwidth = None
+            else:
+                termwidth = self._tw.fullwidth
 
         def show_simple(stat, lines: List[str]) -> None:
             failed = self.stats.get(stat, [])
diff --git a/testing/code/test_excinfo.py b/testing/code/test_excinfo.py
index 2408ab2fdab..0bdb55ece80 100644
--- a/testing/code/test_excinfo.py
+++ b/testing/code/test_excinfo.py
@@ -3,6 +3,7 @@
 import queue
 import sys
 import textwrap
+from io import StringIO
 from typing import Union
 
 import py.path
@@ -1037,10 +1038,11 @@ def f():
         """
         )
         excinfo = pytest.raises(ValueError, mod.f)
-        tw = TerminalWriter(stringio=True)
+        file = StringIO()
+        tw = TerminalWriter(file=file)
         repr = excinfo.getrepr(**reproptions)
         repr.toterminal(tw)
-        assert tw.stringio.getvalue()
+        assert file.getvalue()
 
     def test_traceback_repr_style(self, importasmod, tw_mock):
         mod = importasmod(
@@ -1256,11 +1258,12 @@ def g():
         getattr(excinfo.value, attr).__traceback__ = None
 
         r = excinfo.getrepr()
-        tw = TerminalWriter(stringio=True)
+        file = StringIO()
+        tw = TerminalWriter(file=file)
         tw.hasmarkup = False
         r.toterminal(tw)
 
-        matcher = LineMatcher(tw.stringio.getvalue().splitlines())
+        matcher = LineMatcher(file.getvalue().splitlines())
         matcher.fnmatch_lines(
             [
                 "ValueError: invalid value",