Fixed #1819: Occasional inconsistency with multiple src paths.

isort/settings.py

@@ -458,13 +458,14 @@ def __init__(
         if "src_paths" not in combined_config:
             combined_config["src_paths"] = (path_root / "src", path_root)
         else:
-            src_paths: Set[Path] = set()
+            src_paths: List[Path] = []
             for src_path in combined_config.get("src_paths", ()):
                 full_paths = (
                     path_root.glob(src_path) if "*" in str(src_path) else [path_root / src_path]
                 )
                 for path in full_paths:
-                    src_paths.add(path)
+                    if not path in src_paths:
+                        src_paths.append(path)
 
             combined_config["src_paths"] = tuple(src_paths)
 

tests/unit/test_main.py

@@ -1345,3 +1345,47 @@ def test_multiple_configs(capsys, tmpdir):
     _, err = capsys.readouterr()
 
     assert f"{str(file6)} Imports are incorrectly sorted and/or formatted" in err
+
+
+def test_multiple_src_paths(tmpdir, capsys):
+    """
+    Ensure that isort has consistent behavior with multiple source paths
+    """
+
+    tests_module = tmpdir / "tests"
+    app_module = tmpdir / "app"
+
+    tests_module.mkdir()
+    app_module.mkdir()
+
+    pyproject_toml = tmpdir / "pyproject.toml"
+    pyproject_toml.write_text(
+        """
+[tool.isort]
+profile = "black"
+src_paths = ["app", "tests"]
+auto_identify_namespace_packages = false
+""",
+        "utf-8",
+    )
+    file = tmpdir / "file.py"
+    file.write_text(
+        """
+from app.something import something
+from tests.something import something_else
+""",
+        "utf-8",
+    )
+
+    for _ in range(10):  # To ensure isort has consistent results in multiple runs
+        main.main([str(tmpdir), "--verbose"])
+        out, _ = capsys.readouterr()
+
+        assert (
+            file.read()
+            == """
+from app.something import something
+from tests.something import something_else
+"""
+        )
+        assert "from-type place_module for tests.something returned FIRSTPARTY" in out