No additional newline with --stdout flag. (Sourcery refactored)

CHANGES.rst

@@ -12,6 +12,8 @@ Fixed
 - ``regex`` module now always available for unit tests
 - Compatibility with NixOS. Keep ``$PATH`` intact so Git can be called.
 - Updated tests to pass on new Pygments versions
+- Removed additional newline at the end of the file with the ``--stdout`` flag
+  compared to without.
 
 
 1.3.2_ - 2021-10-28

src/darker/__main__.py

@@ -258,16 +258,32 @@ def print_source(new: TextDocument) -> None:
     """Print the reformatted Python source code"""
     if sys.stdout.isatty():
         try:
-            # pylint: disable=import-outside-toplevel
-            from pygments import highlight
-            from pygments.formatters import TerminalFormatter
-            from pygments.lexers.python import PythonLexer
+            (
+                highlight,
+                TerminalFormatter,  # pylint: disable=invalid-name
+                PythonLexer,
+            ) = _import_pygments()  # type: ignore
         except ImportError:
-            print(new.string)
+            print(new.string, end="")
         else:
-            print(highlight(new.string, PythonLexer(), TerminalFormatter()))
+            print(highlight(new.string, PythonLexer(), TerminalFormatter()), end="")
     else:
-        print(new.string)
+        print(new.string, end="")
+
+
+def _import_pygments():  # type: ignore
+    """Import within a function to ease mocking the import in unit-tests.
+
+    Cannot be typed as it imports parts of its own return type.
+    """
+    # pylint: disable=import-outside-toplevel
+    from pygments import highlight
+    from pygments.formatters import (  # pylint: disable=no-name-in-module
+        TerminalFormatter,
+    )
+    from pygments.lexers.python import PythonLexer
+
+    return highlight, TerminalFormatter, PythonLexer
 
 
 def main(argv: List[str] = None) -> int:
@@ -349,8 +365,7 @@ def main(argv: List[str] = None) -> int:
                 " Either --diff or --check must be used.",
             )
 
-    missing = get_missing_at_revision(paths, revrange.rev2, root)
-    if missing:
+    if missing := get_missing_at_revision(paths, revrange.rev2, root):
         missing_reprs = " ".join(repr(str(path)) for path in missing)
         rev2_repr = "the working tree" if revrange.rev2 == WORKTREE else revrange.rev2
         raise ArgumentError(

src/darker/tests/test_main.py

@@ -8,7 +8,7 @@
 from pathlib import Path
 from textwrap import dedent
 from types import SimpleNamespace
-from unittest.mock import call, patch
+from unittest.mock import Mock, call, patch
 
 import pytest
 from black import find_project_root
@@ -205,7 +205,7 @@ def test_format_edited_parts_all_unchanged(git_repo, monkeypatch):
         )
     )
 
-    assert result == []
+    assert not result
 
 
 def test_format_edited_parts_ast_changed(git_repo, caplog):
@@ -273,7 +273,7 @@ def test_format_edited_parts_isort_on_already_formatted(git_repo):
         report_unmodified=False,
     )
 
-    assert list(result) == []
+    assert not list(result)
 
 
 @pytest.mark.kwparametrize(
@@ -775,11 +775,55 @@ def test_modify_file(tmp_path, new_content, expect):
     assert result == expect
 
 
+@pytest.mark.kwparametrize(
+    dict(
+        new_content=TextDocument(lines=['print("foo")']),
+        tty=False,
+        with_pygments=False,
+        expect=('print("foo")\n',),
+    ),
+    dict(
+        new_content=TextDocument(lines=['print("foo")']),
+        tty=False,
+        with_pygments=True,
+        expect=('print("foo")\n',),
+    ),
+    dict(
+        new_content=TextDocument(lines=['print("foo")']),
+        tty=True,
+        with_pygments=False,
+        expect=('print("foo")\n',),
+    ),
+    dict(
+        new_content=TextDocument(lines=['print("foo")']),
+        tty=True,
+        with_pygments=True,
+        expect=(
+            '\x1b[36mprint\x1b[39;49;00m(\x1b[33m"\x1b[39;49;00mfoo'
+            + '\x1b[33m"\x1b[39;49;00m)\n',
+            '\x1b[36mprint\x1b[39;49;00m(\x1b[33m"\x1b[39;49;00m\x1b[33mfoo'
+            + '\x1b[39;49;00m\x1b[33m"\x1b[39;49;00m)\n',
+        ),
+    ),
+)
+def test_print_source(new_content, tty, with_pygments, expect, capsys):
+    """Highlight is applied only if tty, final newline is handled correctly."""
+    with patch("sys.stdout.isatty", Mock(return_value=tty)), patch(
+        "darker.__main__._import_pygments",
+        Mock(
+            return_value=darker.__main__._import_pygments(),
+            side_effect=None if with_pygments else ImportError(),
+        ),
+    ):
+        darker.__main__.print_source(new_content)
+        assert capsys.readouterr().out in expect
+
+
 def test_stdout_path_resolution(git_repo, capsys):
     """When using ``--stdout``, file paths are resolved correctly"""
     git_repo.add({"src/menu.py": "print ( 'foo' )\n"})
 
     result = darker.__main__.main(["--stdout", "./src/menu.py"])
 
     assert result == 0
-    assert capsys.readouterr().out == 'print("foo")\n\n'
+    assert capsys.readouterr().out == 'print("foo")\n'