test(approvaltests): add postfix parameter to PytestNamer

This enables the usage of the Namer multiple times in one test.

Author: matthiasschaub

approvaltests_config.json

@@ -0,0 +1,3 @@
+{
+  "directory": "tests/approvals"
+}

tests/approvaltests_namers.py

@@ -3,39 +3,47 @@
 
 from approvaltests.namer.namer_base import NamerBase
 
-TEST_DIR = Path(__file__).parent
-APPROVED_DIR = TEST_DIR / "approvals"
-
 
 class PytestNamer(NamerBase):
-    def __init__(self, extension=None):
+    def __init__(self, extension: str = ".txt", postfix: str = ""):
         """An approval tests Namer for naming approved and received files.
 
-        These files will get stored under:
-        `tests/approval/{module}/test_file.py--TestClass--test_func[a]`
-
-        This class uses the `PYTEST_CURRENT_TEST` environment variable, which
-        consist of the node ID and the current stage:
+        This Namer uses the `PYTEST_CURRENT_TEST` environment variable, which
+        consist of the node ID and the current stage to derive names:
         `relative/path/to/test_file.py::TestClass::test_func[a] (call)`
 
-        During a pytest test session, stages can be setup, teardown or call.
-        Approval tests should only be used during the call stage and therefore
-        the ` (call)` postfix is removed.
+        Above example will be translated to:
+        `relative/path/to/test_file.py--TestClass--test_func[a]`
 
-        To avoid the forbidden character `:` in system paths, it is replaced by `-`.
+        Following changes are applied to the `PYTEST_CURRENT_TEST` environmen
+        variables:
+            - To avoid the forbidden character `:` in system paths, it is
+              replaced by `-`.
+            - During a pytest test session, stages can be setup, teardown or
+              call. Approval tests should only be used during the call stage
+              and therefore the ` (call)` postfix is removed.
+
+        If verify is called multiple times use `postfix` parameter to
+        differentiate names.
         """
         self.nodeid: Path = Path(os.environ["PYTEST_CURRENT_TEST"])
+        self.postfix = postfix
         NamerBase.__init__(self, extension)
 
     def get_file_name(self) -> Path:
-        """File name is pytest nodeid w/out directory name and pytest stage."""
-        return Path(str(self.nodeid.name).replace(" (call)", "").replace("::", "-"))
+        """File name is pytest nodeid w/out directory name and pytest."""
+        file_name = str(self.nodeid.name).replace(" (call)", "").replace("::", "-")
+        return Path(file_name) / self.postfix
 
     def get_directory(self) -> Path:
         """Directory is `tests/approval/{module}` derived from pytest nodeid."""
         parts = self.nodeid.parent.parts
         directory = Path(*[p for p in parts if p not in ["tests"]])
-        return APPROVED_DIR / directory
-
-    def get_config(self) -> dict:
-        return {}
+        config = self.get_config()
+        if "directory" in config.keys():
+            return Path(config["directory"]) / directory
+        else:
+            return directory
+
+    def config_directory(self) -> str:
+        return Path(__file__).parent.parent