Add documents and tests for substitution commands

README.rst

@@ -124,6 +124,17 @@ proxy
 max_concurrent
   Max number of concurrent jobs. Default: 20.
 
+Global Options
+--------------
+The following options applies to all checkers.
+
+prefix
+  Strip the prefix string if the version string starts with it.
+
+from_pattern, to_pattern
+  Both are Python-compatible regular expressions. If ``from_pattern`` is found
+  in the version string, it will be replaced with ``to_pattern``
+
 Search in a Webpage
 -------------------
 Search through a specific webpage for the version string. This type of version finding has these fields:

tests/test_substitute.py

@@ -0,0 +1,17 @@
+# MIT licensed
+# Copyright (c) 2013-2017 lilydjwg <lilydjwg@gmail.com>, et al.
+
+import pytest
+pytestmark = pytest.mark.asyncio
+
+async def test_substitute_prefix(get_version):
+    assert await get_version("example", {"manual": "v1.0", "prefix": "v"}) == "1.0"
+
+async def test_substitute_prefix_missing_ok(get_version):
+    assert await get_version("example", {"manual": "1.0", "prefix": "v"}) == "1.0"
+
+async def test_substitute_regex(get_version):
+    assert await get_version("example", {"manual": "r15c", "from_pattern": r"r(\d+)([a-z])", "to_pattern": r"r\1.\2"}) == "r15.c"
+
+async def test_substitute_regex_missing_ok(get_version):
+    assert await get_version("example", {"manual": "r15", "from_pattern": r"r(\d+)([a-z])", "to_pattern": r"r\1.\2"}) == "r15"