Fix bug in careful_copy handling None

The function careful_copy_file was not able to handle None as
a target. Added the functionality as probably originally intended
and added tests.

src/ert/resources/shell_scripts/careful_copy_file.py

@@ -5,13 +5,12 @@
 
 
 def careful_copy_file(src, target=None):
+    if target is None:
+        target = os.path.basename(src)
     if os.path.exists(target):
         print(f"File: {target} already present - not updated")
         return
     if os.path.isfile(src):
-        if target is None:
-            target = os.path.basename(src)
-
         if os.path.isdir(target):
             target_file = os.path.join(target, os.path.basename(src))
             shutil.copyfile(src, target_file)

tests/ert/unit_tests/resources/test_shell.py

@@ -1,6 +1,7 @@
 import contextlib
 import os
 import os.path
+import shutil
 import sys
 from contextlib import suppress
 from pathlib import Path
@@ -471,6 +472,22 @@ def test_copy_file3():
     assert os.path.isfile("rms/output/file.txt")
 
 
+@pytest.mark.usefixtures("use_tmpdir")
+def test_copy_when_target_is_none():
+    Path("somedir").mkdir()
+    Path("somedir/file.txt").write_text("Hei", encoding="utf-8")
+
+    copy_file("somedir/file.txt", None)
+    assert Path("file.txt").read_text(encoding="utf-8") == "Hei"
+
+
+@pytest.mark.usefixtures("use_tmpdir")
+def test_copy_when_target_is_none_in_same_directory():
+    Path("file.txt").write_text("Hei", encoding="utf-8")
+    with pytest.raises(shutil.SameFileError):
+        copy_file("file.txt", None)
+
+
 @pytest.mark.usefixtures("use_tmpdir")
 def test_careful_copy_file():
     with open("file1", "w", encoding="utf-8") as f:
@@ -486,6 +503,31 @@ def test_careful_copy_file():
     assert os.path.isfile("file3")
 
 
+@pytest.mark.usefixtures("use_tmpdir")
+def test_careful_copy_file_when_target_is_none():
+    Path("somedir").mkdir()
+    Path("somedir/file.txt").write_text("Hei", encoding="utf-8")
+
+    careful_copy_file("somedir/file.txt", None)
+    assert Path("file.txt").read_text(encoding="utf-8") == "Hei"
+
+
+@pytest.mark.usefixtures("use_tmpdir")
+def test_careful_copy_when_target_is_none_in_same_directory_is_noop():
+    Path("file.txt").write_text("Hei", encoding="utf-8")
+    careful_copy_file("file.txt", None)  # File will not be touched
+    assert Path("file.txt").read_text(encoding="utf-8") == "Hei"
+
+
+@pytest.mark.usefixtures("use_tmpdir")
+def test_careful_copy_when_target_is_none_does_not_touch_existing():
+    Path("somedir").mkdir()
+    Path("somedir/file.txt").write_text("Hei", encoding="utf-8")
+    Path("file.txt").write_text("I will survive", encoding="utf-8")
+    careful_copy_file("somedir/file.txt", None)
+    assert Path("file.txt").read_text(encoding="utf-8") == "I will survive"
+
+
 @pytest.fixture
 def minimal_case(tmpdir):
     with tmpdir.as_cwd():