diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 116122b6f99..20cf309baac 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -21,6 +21,9 @@ concurrency:
   group: tests-${{ github.head_ref || github.ref }}
   cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
+env:
+  PYTHONWARNDEFAULTENCODING: 'true'
+
 jobs:
   tests:
     name: ${{ matrix.os }} / ${{ matrix.python-version }}
diff --git a/src/poetry/masonry/builders/editable.py b/src/poetry/masonry/builders/editable.py
index 076843ab3db..f54d1e6aa63 100644
--- a/src/poetry/masonry/builders/editable.py
+++ b/src/poetry/masonry/builders/editable.py
@@ -234,7 +234,8 @@ def _add_dist_info(self, added_files: list[Path]) -> None:
             json.dumps({
                 "dir_info": {"editable": True},
                 "url": self._poetry.file.path.parent.absolute().as_uri(),
-            })
+            }),
+            encoding="utf-8",
         )
         added_files.append(direct_url_json)
 
diff --git a/src/poetry/repositories/installed_repository.py b/src/poetry/repositories/installed_repository.py
index 1eb6b1d9742..a75c1bb7912 100644
--- a/src/poetry/repositories/installed_repository.py
+++ b/src/poetry/repositories/installed_repository.py
@@ -58,7 +58,7 @@ def get_package_paths(cls, env: Env, name: str) -> set[Path]:
             if not pth_file.exists():
                 continue
 
-            with pth_file.open() as f:
+            with pth_file.open(encoding="utf-8") as f:
                 for line in f:
                     line = line.strip()
                     if line and not line.startswith(("#", "import ", "import\t")):
diff --git a/src/poetry/utils/env/base_env.py b/src/poetry/utils/env/base_env.py
index 0880502cf41..07583049dc0 100644
--- a/src/poetry/utils/env/base_env.py
+++ b/src/poetry/utils/env/base_env.py
@@ -348,7 +348,7 @@ def _run(self, cmd: list[str], **kwargs: Any) -> str:
                 output = ""
             else:
                 output = subprocess.check_output(
-                    cmd, stderr=stderr, env=env, text=True, **kwargs
+                    cmd, stderr=stderr, env=env, text=True, encoding="utf-8", **kwargs
                 )
         except CalledProcessError as e:
             raise EnvCommandError(e)
diff --git a/src/poetry/utils/env/virtual_env.py b/src/poetry/utils/env/virtual_env.py
index 8a573426fec..7d568145fa5 100644
--- a/src/poetry/utils/env/virtual_env.py
+++ b/src/poetry/utils/env/virtual_env.py
@@ -143,7 +143,7 @@ def includes_system_site_packages(self) -> bool:
         return pyvenv_cfg.exists() and (
             re.search(
                 r"^\s*include-system-site-packages\s*=\s*true\s*$",
-                pyvenv_cfg.read_text(),
+                pyvenv_cfg.read_text(encoding="utf-8"),
                 re.IGNORECASE | re.MULTILINE,
             )
             is not None
diff --git a/src/poetry/utils/setup_reader.py b/src/poetry/utils/setup_reader.py
index ffc10a13a87..4728f676d14 100644
--- a/src/poetry/utils/setup_reader.py
+++ b/src/poetry/utils/setup_reader.py
@@ -75,7 +75,7 @@ def read_setup_py(self, filepath: Path) -> dict[str, Any]:
     def read_setup_cfg(self, filepath: Path) -> dict[str, Any]:
         parser = ConfigParser()
 
-        parser.read(str(filepath))
+        parser.read(str(filepath), encoding="utf-8")
 
         name = None
         version = None
diff --git a/tests/console/commands/env/test_remove.py b/tests/console/commands/env/test_remove.py
index 38998f92634..b3f8da37797 100644
--- a/tests/console/commands/env/test_remove.py
+++ b/tests/console/commands/env/test_remove.py
@@ -76,13 +76,18 @@ def test_remove_all(
     if envs_file == "empty":
         envs_file_path.touch()
     elif envs_file == "self":
-        envs_file_path.write_text(f'[{venv_name}]\nminor = "3.9"\npatch = "3.9.1"\n')
+        envs_file_path.write_text(
+            f'[{venv_name}]\nminor = "3.9"\npatch = "3.9.1"\n', encoding="utf-8"
+        )
     elif envs_file == "other":
-        envs_file_path.write_text('[other-abcdefgh]\nminor = "3.9"\npatch = "3.9.1"\n')
+        envs_file_path.write_text(
+            '[other-abcdefgh]\nminor = "3.9"\npatch = "3.9.1"\n', encoding="utf-8"
+        )
     elif envs_file == "self_and_other":
         envs_file_path.write_text(
             f'[{venv_name}]\nminor = "3.9"\npatch = "3.9.1"\n'
-            '[other-abcdefgh]\nminor = "3.9"\npatch = "3.9.1"\n'
+            '[other-abcdefgh]\nminor = "3.9"\npatch = "3.9.1"\n',
+            encoding="utf-8",
         )
     else:
         # no envs file -> nothing to prepare
@@ -97,7 +102,7 @@ def test_remove_all(
 
     if envs_file is not None:
         assert envs_file_path.exists()
-        envs_file_content = envs_file_path.read_text()
+        envs_file_content = envs_file_path.read_text(encoding="utf-8")
         assert venv_name not in envs_file_content
         if "other" in envs_file:
             assert "other-abcdefgh" in envs_file_content
diff --git a/tests/console/commands/self/test_self_command.py b/tests/console/commands/self/test_self_command.py
index 7abf266ed7e..e38cee61873 100644
--- a/tests/console/commands/self/test_self_command.py
+++ b/tests/console/commands/self/test_self_command.py
@@ -29,9 +29,11 @@ def test_generate_system_pyproject_trailing_newline(
     example_system_pyproject: str,
 ) -> None:
     cmd = SelfCommand()
-    cmd.system_pyproject.write_text(example_system_pyproject + "\n" * existing_newlines)
+    cmd.system_pyproject.write_text(
+        example_system_pyproject + "\n" * existing_newlines, encoding="utf-8"
+    )
     cmd.generate_system_pyproject()
-    generated = cmd.system_pyproject.read_text()
+    generated = cmd.system_pyproject.read_text(encoding="utf-8")
 
     assert len(generated) - len(generated.rstrip("\n")) == existing_newlines
 
@@ -40,10 +42,12 @@ def test_generate_system_pyproject_carriage_returns(
     example_system_pyproject: str,
 ) -> None:
     cmd = SelfCommand()
-    cmd.system_pyproject.write_text(example_system_pyproject + "\n")
+    cmd.system_pyproject.write_text(example_system_pyproject + "\n", encoding="utf-8")
     cmd.generate_system_pyproject()
 
-    with open(cmd.system_pyproject, newline="") as f:  # do not translate newlines
+    with open(
+        cmd.system_pyproject, newline="", encoding="utf-8"
+    ) as f:  # do not translate newlines
         generated = f.read()
 
     assert "\r\r" not in generated
diff --git a/tests/console/commands/test_init.py b/tests/console/commands/test_init.py
index f18570a4eed..4919f94b2fa 100644
--- a/tests/console/commands/test_init.py
+++ b/tests/console/commands/test_init.py
@@ -122,7 +122,7 @@ def test_noninteractive(
     assert tester.io.fetch_output() == expected
     assert tester.io.fetch_error() == ""
 
-    toml_content = (tmp_path / "pyproject.toml").read_text()
+    toml_content = (tmp_path / "pyproject.toml").read_text(encoding="utf-8")
     assert 'name = "my-package"' in toml_content
     assert 'pytest = "^3.6.0"' in toml_content
 
@@ -884,9 +884,11 @@ def test_init_existing_pyproject_simple(
 [tool.black]
 line-length = 88
 """
-    pyproject_file.write_text(existing_section)
+    pyproject_file.write_text(existing_section, encoding="utf-8")
     tester.execute(inputs=init_basic_inputs)
-    assert f"{existing_section}\n{init_basic_toml}" in pyproject_file.read_text()
+    assert f"{existing_section}\n{init_basic_toml}" in pyproject_file.read_text(
+        encoding="utf-8"
+    )
 
 
 @pytest.mark.parametrize("linesep", ["\n", "\r\n"])
@@ -902,10 +904,10 @@ def test_init_existing_pyproject_consistent_linesep(
 [tool.black]
 line-length = 88
 """.replace("\n", linesep)
-    with open(pyproject_file, "w", newline="") as f:
+    with open(pyproject_file, "w", newline="", encoding="utf-8") as f:
         f.write(existing_section)
     tester.execute(inputs=init_basic_inputs)
-    with open(pyproject_file, newline="") as f:
+    with open(pyproject_file, newline="", encoding="utf-8") as f:
         content = f.read()
     init_basic_toml = init_basic_toml.replace("\n", linesep)
     assert f"{existing_section}{linesep}{init_basic_toml}" in content
@@ -922,7 +924,7 @@ def test_init_non_interactive_existing_pyproject_add_dependency(
 [tool.black]
 line-length = 88
 """
-    pyproject_file.write_text(existing_section)
+    pyproject_file.write_text(existing_section, encoding="utf-8")
 
     repo.add_package(get_package("foo", "1.19.2"))
 
@@ -946,7 +948,9 @@ def test_init_non_interactive_existing_pyproject_add_dependency(
 python = "^3.6"
 foo = "^1.19.2"
 """
-    assert f"{existing_section}\n{expected}" in pyproject_file.read_text()
+    assert f"{existing_section}\n{expected}" in pyproject_file.read_text(
+        encoding="utf-8"
+    )
 
 
 def test_init_existing_pyproject_with_build_system_fails(
@@ -958,13 +962,13 @@ def test_init_existing_pyproject_with_build_system_fails(
 requires = ["setuptools >= 40.6.0", "wheel"]
 build-backend = "setuptools.build_meta"
 """
-    pyproject_file.write_text(existing_section)
+    pyproject_file.write_text(existing_section, encoding="utf-8")
     tester.execute(inputs=init_basic_inputs)
     assert (
         tester.io.fetch_error().strip()
         == "A pyproject.toml file with a defined build-system already exists."
     )
-    assert existing_section in pyproject_file.read_text()
+    assert existing_section in pyproject_file.read_text(encoding="utf-8")
 
 
 @pytest.mark.parametrize(
@@ -1100,7 +1104,7 @@ def mock_check_output(cmd: str, *_: Any, **__: Any) -> str:
 python = "^{python}"
 """
 
-    assert expected in pyproject_file.read_text()
+    assert expected in pyproject_file.read_text(encoding="utf-8")
 
 
 def test_get_pool(mocker: MockerFixture, source_dir: Path) -> None:
diff --git a/tests/console/commands/test_new.py b/tests/console/commands/test_new.py
index 9bbef7fff17..11654fd535e 100644
--- a/tests/console/commands/test_new.py
+++ b/tests/console/commands/test_new.py
@@ -228,4 +228,4 @@ def mock_check_output(cmd: str, *_: Any, **__: Any) -> str:
 python = "^{python}"
 """
 
-    assert expected in pyproject_file.read_text()
+    assert expected in pyproject_file.read_text(encoding="utf-8")
diff --git a/tests/console/commands/test_version.py b/tests/console/commands/test_version.py
index 4772a400be1..5741cf3d9f5 100644
--- a/tests/console/commands/test_version.py
+++ b/tests/console/commands/test_version.py
@@ -126,9 +126,9 @@ def test_phase_version_update(tester: CommandTester) -> None:
 
 def test_dry_run(tester: CommandTester) -> None:
     assert isinstance(tester.command, VersionCommand)
-    old_pyproject = tester.command.poetry.file.path.read_text()
+    old_pyproject = tester.command.poetry.file.path.read_text(encoding="utf-8")
     tester.execute("--dry-run major")
 
-    new_pyproject = tester.command.poetry.file.path.read_text()
+    new_pyproject = tester.command.poetry.file.path.read_text(encoding="utf-8")
     assert tester.io.fetch_output() == "Bumping version from 1.2.3 to 2.0.0\n"
     assert old_pyproject == new_pyproject
diff --git a/tests/inspection/test_info.py b/tests/inspection/test_info.py
index 933d48a7f0e..4877d1afe56 100644
--- a/tests/inspection/test_info.py
+++ b/tests/inspection/test_info.py
@@ -61,7 +61,8 @@ def demo_setup(source_dir: Path) -> Path:
         "from setuptools import setup; "
         'setup(name="demo", '
         'version="0.1.0", '
-        'install_requires=["package"])'
+        'install_requires=["package"])',
+        encoding="utf-8",
     )
     return source_dir
 
@@ -76,7 +77,8 @@ def demo_setup_cfg(source_dir: Path) -> Path:
             "version = 0.1.0",
             "[options]",
             "install_requires = package",
-        ])
+        ]),
+        encoding="utf-8",
     )
     return source_dir
 
@@ -88,7 +90,8 @@ def demo_setup_complex(source_dir: Path) -> Path:
         "from setuptools import setup; "
         'setup(name="demo", '
         'version="0.1.0", '
-        'install_requires=[i for i in ["package"]])'
+        'install_requires=[i for i in ["package"]])',
+        encoding="utf-8",
     )
     return source_dir
 
@@ -96,7 +99,9 @@ def demo_setup_complex(source_dir: Path) -> Path:
 @pytest.fixture
 def demo_setup_complex_pep517_legacy(demo_setup_complex: Path) -> Path:
     pyproject_toml = demo_setup_complex / "pyproject.toml"
-    pyproject_toml.write_text('[build-system]\nrequires = ["setuptools", "wheel"]')
+    pyproject_toml.write_text(
+        '[build-system]\nrequires = ["setuptools", "wheel"]', encoding="utf-8"
+    )
     return demo_setup_complex
 
 
@@ -109,20 +114,26 @@ def demo_setup_complex_calls_script(
     shutil.copytree(fixture_dir("scripts"), scripts_dir)
 
     pyproject = source_dir / "pyproject.toml"
-    pyproject.write_text(f"""\
+    pyproject.write_text(
+        f"""\
     [build-system]
     requires = ["setuptools", "scripts @ {scripts_dir.as_uri()}"]
     build-backend = "setuptools.build_meta:__legacy__"
-""")
+""",
+        encoding="utf-8",
+    )
 
     setup_py = source_dir / "setup.py"
-    setup_py.write_text("""\
+    setup_py.write_text(
+        """\
 import subprocess
 from setuptools import setup
 if subprocess.call(["exit-code"]) != 42:
     raise RuntimeError("Wrong exit code.")
 setup(name="demo", version="0.1.0", install_requires=[i for i in ["package"]])
-""")
+""",
+        encoding="utf-8",
+    )
 
     return source_dir
 
@@ -327,7 +338,7 @@ def test_info_setup_missing_mandatory_should_trigger_pep517(
     setup += ")"
 
     setup_py = source_dir / "setup.py"
-    setup_py.write_text(setup)
+    setup_py.write_text(setup, encoding="utf-8")
 
     spy = mocker.spy(VirtualEnv, "run")
     _ = PackageInfo.from_directory(source_dir)
diff --git a/tests/installation/test_wheel_installer.py b/tests/installation/test_wheel_installer.py
index b7b3d7c7c93..f74166fdb8c 100644
--- a/tests/installation/test_wheel_installer.py
+++ b/tests/installation/test_wheel_installer.py
@@ -54,7 +54,7 @@ def test_default_installation_dist_info_dir_content(default_installation: Path)
 
 def test_installer_file_contains_valid_version(default_installation: Path) -> None:
     installer_file = default_installation / "demo-0.1.0.dist-info" / "INSTALLER"
-    with open(installer_file) as f:
+    with open(installer_file, encoding="utf-8") as f:
         installer_content = f.read()
     match = re.match(r"Poetry (?P<version>.*)", installer_content)
     assert match
diff --git a/tests/masonry/builders/test_editable_builder.py b/tests/masonry/builders/test_editable_builder.py
index aa7e9e03ef7..bc92569720e 100644
--- a/tests/masonry/builders/test_editable_builder.py
+++ b/tests/masonry/builders/test_editable_builder.py
@@ -98,7 +98,9 @@ def test_builder_installs_proper_files_for_standard_packages(
     assert tmp_venv.site_packages.exists(pth_file)
     assert (
         simple_poetry.file.path.parent.resolve().as_posix()
-        == tmp_venv.site_packages.find(pth_file)[0].read_text().strip(os.linesep)
+        == tmp_venv.site_packages.find(pth_file)[0]
+        .read_text(encoding="utf-8")
+        .strip(os.linesep)
     )
 
     dist_info = Path("simple_project-1.2.3.dist-info")
@@ -117,12 +119,12 @@ def test_builder_installs_proper_files_for_standard_packages(
             "dir_info": {"editable": True},
             "url": simple_poetry.file.path.parent.as_uri(),
         },
-        json.loads(dist_info.joinpath("direct_url.json").read_text()),
+        json.loads(dist_info.joinpath("direct_url.json").read_text(encoding="utf-8")),
     )
 
-    assert dist_info.joinpath("INSTALLER").read_text() == "poetry"
+    assert dist_info.joinpath("INSTALLER").read_text(encoding="utf-8") == "poetry"
     assert (
-        dist_info.joinpath("entry_points.txt").read_text()
+        dist_info.joinpath("entry_points.txt").read_text(encoding="utf-8")
         == "[console_scripts]\nbaz=bar:baz.boom.bim\nfoo=foo:bar\n"
         "fox=fuz.foo:bar.baz\n\n"
     )
@@ -184,7 +186,7 @@ def test_builder_installs_proper_files_for_standard_packages(
     sys.exit(baz.boom.bim())
 """
 
-    assert baz_script == tmp_venv._bin_dir.joinpath("baz").read_text()
+    assert baz_script == tmp_venv._bin_dir.joinpath("baz").read_text(encoding="utf-8")
 
     foo_script = f"""\
 #!{tmp_venv.python}
@@ -195,7 +197,7 @@ def test_builder_installs_proper_files_for_standard_packages(
     sys.exit(bar())
 """
 
-    assert foo_script == tmp_venv._bin_dir.joinpath("foo").read_text()
+    assert foo_script == tmp_venv._bin_dir.joinpath("foo").read_text(encoding="utf-8")
 
     fox_script = f"""\
 #!{tmp_venv.python}
@@ -206,7 +208,7 @@ def test_builder_installs_proper_files_for_standard_packages(
     sys.exit(bar.baz())
 """
 
-    assert fox_script == tmp_venv._bin_dir.joinpath("fox").read_text()
+    assert fox_script == tmp_venv._bin_dir.joinpath("fox").read_text(encoding="utf-8")
 
 
 def test_builder_falls_back_on_setup_and_pip_for_packages_with_build_scripts(
diff --git a/tests/pyproject/conftest.py b/tests/pyproject/conftest.py
index 82ff2198389..8aceff30d8c 100644
--- a/tests/pyproject/conftest.py
+++ b/tests/pyproject/conftest.py
@@ -12,7 +12,7 @@
 @pytest.fixture
 def pyproject_toml(tmp_path: Path) -> Path:
     path = tmp_path / "pyproject.toml"
-    with path.open(mode="w"):
+    with path.open(mode="w", encoding="utf-8"):
         pass
     return path
 
@@ -24,7 +24,7 @@ def build_system_section(pyproject_toml: Path) -> str:
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"
 """
-    with pyproject_toml.open(mode="a") as f:
+    with pyproject_toml.open(mode="a", encoding="utf-8") as f:
         f.write(content)
     return content
 
@@ -38,6 +38,6 @@ def poetry_section(pyproject_toml: Path) -> str:
 [tool.poetry.dependencies]
 python = "^3.5"
 """
-    with pyproject_toml.open(mode="a") as f:
+    with pyproject_toml.open(mode="a", encoding="utf-8") as f:
         f.write(content)
     return content
diff --git a/tests/pyproject/test_pyproject_toml_file.py b/tests/pyproject/test_pyproject_toml_file.py
index 5cb1b8c4327..e8fea9000ec 100644
--- a/tests/pyproject/test_pyproject_toml_file.py
+++ b/tests/pyproject/test_pyproject_toml_file.py
@@ -14,7 +14,7 @@
 
 
 def test_pyproject_toml_file_invalid(pyproject_toml: Path) -> None:
-    with pyproject_toml.open(mode="a") as f:
+    with pyproject_toml.open(mode="a", encoding="utf-8") as f:
         f.write("<<<<<<<<<<<")
 
     with pytest.raises(PoetryCoreException) as excval:
diff --git a/tests/utils/env/test_env.py b/tests/utils/env/test_env.py
index da481455b55..0386f333b67 100644
--- a/tests/utils/env/test_env.py
+++ b/tests/utils/env/test_env.py
@@ -178,11 +178,14 @@ def test_call_does_not_block_on_full_pipe(
 ) -> None:
     """see https://github.com/python-poetry/poetry/issues/7698"""
     script = tmp_path / "script.py"
-    script.write_text(f"""\
+    script.write_text(
+        f"""\
 import sys
 for i in range(10000):
     print('just print a lot of text to fill the buffer', file={out})
-""")
+""",
+        encoding="utf-8",
+    )
 
     def target(result: list[int]) -> None:
         tmp_venv.run("python", str(script), call=True)
@@ -271,7 +274,7 @@ def test_env_system_packages(
 
     assert (
         f"include-system-site-packages = {str(with_system_site_packages).lower()}"
-        in pyvenv_cfg.read_text()
+        in pyvenv_cfg.read_text(encoding="utf-8")
     )
     assert env.includes_system_site_packages is with_system_site_packages
 
diff --git a/tests/utils/test_cache.py b/tests/utils/test_cache.py
index 1f4abfd4974..7c878586780 100644
--- a/tests/utils/test_cache.py
+++ b/tests/utils/test_cache.py
@@ -167,9 +167,12 @@ def test_detect_corrupted_cache_key_file(
 
     # original content: 9999999999"value"
 
-    write_modes = {str: "w", bytes: "wb"}
-    with open(key1_path, write_modes[type(corrupt_payload)]) as f:
-        f.write(corrupt_payload)  # write corrupt data
+    if isinstance(corrupt_payload, str):
+        with open(key1_path, "w", encoding="utf-8") as f:
+            f.write(corrupt_payload)  # write corrupt data
+    else:
+        with open(key1_path, "wb") as f:
+            f.write(corrupt_payload)  # write corrupt data
 
     assert poetry_file_cache.get("key1") is None
 
@@ -333,7 +336,7 @@ def test_get_cached_archive_for_link_no_race_condition(
     def replace_file(_: str, dest: Path) -> None:
         dest.unlink(missing_ok=True)
         # write some data (so it takes a while) to provoke possible race conditions
-        dest.write_text("a" * 2**20)
+        dest.write_text("a" * 2**20, encoding="utf-8")
 
     download_mock = mocker.Mock(side_effect=replace_file)
 
diff --git a/tests/vcs/git/test_system.py b/tests/vcs/git/test_system.py
index 2491939c64f..5763b3607da 100644
--- a/tests/vcs/git/test_system.py
+++ b/tests/vcs/git/test_system.py
@@ -23,6 +23,7 @@ def get_head_sha(cwd: Path) -> str:
         ["git", "rev-parse", "HEAD"],
         cwd=cwd,
         text=True,
+        encoding="utf-8",
     ).strip()
 
 
@@ -39,7 +40,7 @@ def temp_repo(tmp_path: Path) -> TempRepoFixture:
     repo = dulwich.repo.Repo.init(str(tmp_path))
 
     # init commit
-    (tmp_path / "foo").write_text("foo")
+    (tmp_path / "foo").write_text("foo", encoding="utf-8")
     repo.stage(["foo"])
 
     init_commit = repo.do_commit(
@@ -50,7 +51,7 @@ def temp_repo(tmp_path: Path) -> TempRepoFixture:
     )
 
     # extra commit
-    (tmp_path / "foo").write_text("bar")
+    (tmp_path / "foo").write_text("bar", encoding="utf-8")
     repo.stage(["foo"])
 
     head_commit = repo.do_commit(