test: Move make_fake_input_tree to testutil

This is useful for other stage tests, move it and add a test.

osbuild/testutil/__init__.py

@@ -1,6 +1,7 @@
 """
 Test related utilities
 """
+import os
 import shutil
 
 
@@ -13,3 +14,20 @@ def assert_dict_has(v, keys, expected_value):
         assert key in v
         v = v[key]
     assert v == expected_value
+
+
+def make_fake_input_tree(tmpdir, fake_content: dict) -> str:
+    """Create a directory tree of files with content.
+
+    Call it with:
+        {"filename": "content", "otherfile": "content"}
+
+    filename paths will have their parents created as needed, under tmpdir.
+    """
+    basedir = os.path.join(tmpdir, "tree")
+    for path, content in fake_content.items():
+        dirp, name = os.path.split(os.path.join(basedir, path.lstrip("/")))
+        os.makedirs(dirp, exist_ok=True)
+        with open(os.path.join(dirp, name), "w", encoding="utf-8") as fp:
+            fp.write(content)
+    return basedir

stages/test/test_erofs.py

@@ -7,20 +7,9 @@ from unittest import mock
 import pytest
 
 import osbuild.meta
-from osbuild.testutil import has_executable
+from osbuild.testutil import has_executable, make_fake_input_tree
 from osbuild.testutil.imports import import_module_from_path
 
-
-def make_fake_input_tree(tmpdir, fake_content: dict) -> str:
-    basedir = os.path.join(tmpdir, "tree")
-    for path, content in fake_content.items():
-        dirp, name = os.path.split(os.path.join(basedir, path.lstrip("/")))
-        os.makedirs(dirp, exist_ok=True)
-        with open(os.path.join(dirp, name), "w", encoding="utf-8") as fp:
-            fp.write(content)
-    return basedir
-
-
 TEST_INPUT = [
     ({}, []),
     ({"compression": {"method": "lz4"}}, ["-z", "lz4"]),

test/mod/test_testutil_fake_tree.py

@@ -0,0 +1,20 @@
+#
+# Tests for the 'osbuild.util.testutil' module.
+#
+import os.path
+
+import pytest
+
+from osbuild.testutil import make_fake_input_tree
+
+
+def test_make_fake_tree(tmp_path):  # pylint: disable=unused-argument
+    fake_input_tree = make_fake_input_tree(tmp_path, {
+        "/fake-file-one": "Some content",
+        "/second/fake-file-two": "Second content",
+    })
+    assert os.path.isdir(fake_input_tree)
+    assert os.path.exists(os.path.join(fake_input_tree, "fake-file-one"))
+    assert open(os.path.join(fake_input_tree, "fake-file-one")).read() == "Some content"
+    assert os.path.exists(os.path.join(fake_input_tree, "second/fake-file-two"))
+    assert open(os.path.join(fake_input_tree, "second/fake-file-two")).read() == "Second content"