diff --git a/src/versioningit/onbuild.py b/src/versioningit/onbuild.py
index b992fd1..496193b 100644
--- a/src/versioningit/onbuild.py
+++ b/src/versioningit/onbuild.py
@@ -112,14 +112,17 @@ def open(
         p = self.provider.build_dir / path
         if ("w" in mode or "a" in mode) and path not in self.provider.modified:
             self.provider.modified.add(path)
+            p.parent.mkdir(parents=True, exist_ok=True)
             # If setuptools is using hard links for the build files, undo that
             # for this file:
-            with suppress(FileNotFoundError):
+            try:
                 p.unlink()
-            p.parent.mkdir(parents=True, exist_ok=True)
-            if not p.exists() and "a" in mode:
-                with suppress(FileNotFoundError):
-                    shutil.copy2(self.provider.src_dir / self.source_path, p)
+            except FileNotFoundError:
+                pass
+            else:
+                if "a" in mode:
+                    with suppress(FileNotFoundError):
+                        shutil.copy2(self.provider.src_dir / self.source_path, p)
         return p.open(mode=mode, encoding=encoding, errors=errors, newline=newline)
 
 
diff --git a/test/test_methods/test_onbuild.py b/test/test_methods/test_onbuild.py
index da79716..1211ba1 100644
--- a/test/test_methods/test_onbuild.py
+++ b/test/test_methods/test_onbuild.py
@@ -1,11 +1,20 @@
 from __future__ import annotations
 from datetime import datetime, timezone
+import os
 from pathlib import Path
 from shutil import copytree
-from typing import Any
+from typing import TYPE_CHECKING, Any
 import pytest
 from versioningit.errors import ConfigError
-from versioningit.onbuild import SetuptoolsFileProvider, replace_version_onbuild
+from versioningit.onbuild import (
+    FileProvider,
+    HatchFileProvider,
+    SetuptoolsFileProvider,
+    replace_version_onbuild,
+)
+
+if TYPE_CHECKING:
+    from typing_extensions import Literal
 
 DATA_DIR = Path(__file__).parent.with_name("data")
 
@@ -251,3 +260,158 @@ def test_replace_version_onbuild_version_not_captured(tmp_path: Path) -> None:
     )
     for p in tmp_path.iterdir():
         assert p.read_bytes() == (src_dir / p.name).read_bytes()
+
+
+@pytest.mark.parametrize("is_source", [False, True])
+@pytest.mark.parametrize(
+    "mode,after",
+    [
+        ("w", "Coconut\n"),
+        ("a", "Apple\nCoconut\n"),
+    ],
+)
+def test_setuptools_file_provider_read_write_read(
+    is_source: bool, mode: Literal["w", "a"], after: str, tmp_path: Path
+) -> None:
+    src_dir = tmp_path / "src"
+    src_dir.mkdir()
+    build_dir = tmp_path / "build"
+    build_dir.mkdir()
+    (src_dir / "apple.txt").write_text("Apple\n")
+    (build_dir / "apple.txt").write_text("Macintosh\n")
+    (build_dir / "banana.txt").write_text("Banana\n")
+    provider = SetuptoolsFileProvider(src_dir=src_dir, build_dir=build_dir)
+    file = provider.get_file(
+        source_path="apple.txt", build_path="banana.txt", is_source=is_source
+    )
+    with file.open() as fp:
+        contents = fp.read()
+    if is_source:
+        assert contents == "Macintosh\n"
+    else:
+        assert contents == "Banana\n"
+    with file.open(mode) as fp:
+        fp.write("Coconut\n")
+    with file.open() as fp:
+        contents = fp.read()
+    assert contents == after
+    assert (src_dir / "apple.txt").read_text() == "Apple\n"
+    if is_source:
+        assert (build_dir / "apple.txt").read_text() == after
+        assert (build_dir / "banana.txt").read_text() == "Banana\n"
+    else:
+        assert (build_dir / "apple.txt").read_text() == "Macintosh\n"
+        assert (build_dir / "banana.txt").read_text() == after
+
+
+@pytest.mark.parametrize("is_source", [False, True])
+@pytest.mark.parametrize(
+    "mode,after",
+    [
+        ("w", "Coconut\n"),
+        ("a", "Apple\nCoconut\n"),
+    ],
+)
+def test_setuptools_file_provider_read_write_read_hard_link(
+    is_source: bool, mode: Literal["w", "a"], after: str, tmp_path: Path
+) -> None:
+    src_dir = tmp_path / "src"
+    src_dir.mkdir()
+    build_dir = tmp_path / "build"
+    build_dir.mkdir()
+    (src_dir / "apple.txt").write_text("Apple\n")
+    if is_source:
+        os.link(src_dir / "apple.txt", build_dir / "apple.txt")
+    else:
+        os.link(src_dir / "apple.txt", build_dir / "banana.txt")
+    provider = SetuptoolsFileProvider(src_dir=src_dir, build_dir=build_dir)
+    file = provider.get_file(
+        source_path="apple.txt", build_path="banana.txt", is_source=is_source
+    )
+    with file.open() as fp:
+        contents = fp.read()
+    assert contents == "Apple\n"
+    with file.open(mode) as fp:
+        fp.write("Coconut\n")
+    with file.open() as fp:
+        contents = fp.read()
+    assert contents == after
+    assert (src_dir / "apple.txt").read_text() == "Apple\n"
+    if is_source:
+        assert (build_dir / "apple.txt").read_text() == after
+        assert not (build_dir / "banana.txt").exists()
+    else:
+        assert not (build_dir / "apple.txt").exists()
+        assert (build_dir / "banana.txt").read_text() == after
+
+
+@pytest.mark.parametrize("is_source", [False, True])
+@pytest.mark.parametrize(
+    "mode,after",
+    [
+        ("w", "Banana\n"),
+        ("a", "Apple\nBanana\n"),
+    ],
+)
+def test_hatch_file_provider_read_write_read(
+    is_source: bool, mode: Literal["w", "a"], after: str, tmp_path: Path
+) -> None:
+    src_dir = tmp_path / "src"
+    src_dir.mkdir()
+    tmp_dir = tmp_path / "tmp"
+    tmp_dir.mkdir()
+    (src_dir / "apple.txt").write_text("Apple\n")
+    provider = HatchFileProvider(src_dir=src_dir, tmp_dir=tmp_dir)
+    file = provider.get_file(
+        source_path="apple.txt", build_path="banana.txt", is_source=is_source
+    )
+    with file.open() as fp:
+        contents = fp.read()
+    assert contents == "Apple\n"
+    with file.open(mode) as fp:
+        fp.write("Banana\n")
+    with file.open() as fp:
+        contents = fp.read()
+    assert contents == after
+    assert (src_dir / "apple.txt").read_text() == "Apple\n"
+    if is_source:
+        assert (tmp_dir / "apple.txt").read_text() == after
+        assert not (tmp_dir / "banana.txt").exists()
+    else:
+        assert not (tmp_dir / "apple.txt").exists()
+        assert (tmp_dir / "banana.txt").read_text() == after
+
+
+@pytest.mark.parametrize("backend", ["setuptools", "hatch"])
+@pytest.mark.parametrize("is_source", [False, True])
+@pytest.mark.parametrize("mode", ["w", "a"])
+def test_file_provider_write_new_file(
+    backend: str, is_source: bool, mode: Literal["w", "a"], tmp_path: Path
+) -> None:
+    src_dir = tmp_path / "src"
+    src_dir.mkdir()
+    build_dir = tmp_path / "build"
+    build_dir.mkdir()
+    provider: FileProvider
+    if backend == "setuptools":
+        provider = SetuptoolsFileProvider(src_dir=src_dir, build_dir=build_dir)
+    else:
+        assert backend == "hatch"
+        provider = HatchFileProvider(src_dir=src_dir, tmp_dir=build_dir)
+    file = provider.get_file(
+        source_path="green/apple.txt",
+        build_path="yellow/banana.txt",
+        is_source=is_source,
+    )
+    with file.open(mode) as fp:
+        fp.write("Coconut\n")
+    with file.open() as fp:
+        contents = fp.read()
+    assert contents == "Coconut\n"
+    assert not (src_dir / "green" / "apple.txt").exists()
+    if is_source:
+        assert (build_dir / "green" / "apple.txt").read_text() == "Coconut\n"
+        assert not (build_dir / "yellow" / "banana.txt").exists()
+    else:
+        assert not (build_dir / "green" / "apple.txt").exists()
+        assert (build_dir / "yellow" / "banana.txt").read_text() == "Coconut\n"