fix: process cases that multiple parsers found for given type, etc.

process cases that multiple parsers found for given type, file extension
and so such as JSON and YAML. The previous code expects there is no such
cases and that causes exceptions.

tests/api.py

@@ -17,6 +17,7 @@
 import anyconfig.backend.json
 import anyconfig.compat
 import anyconfig.dicts
+import anyconfig.processors
 import anyconfig.template
 import tests.common
 
@@ -84,17 +85,32 @@ def _is_file_object(obj):
 
 class Test_10_find_loader(unittest.TestCase):
 
-    def _assert_isinstance(self, obj, cls, msg=False):
-        self.assertTrue(isinstance(obj, cls), msg or repr(obj))
+    psrs = anyconfig.backends.Parsers().list()
+
+    def _assert_isinstances(self, obj, clss, msg=False):
+        self.assertTrue(any(isinstance(obj, cls) for cls in clss),
+                        msg or "%r vs %r" % (obj, clss))
+
+    def test_10_find_loader__w_parser_type_or_instance(self):
+        def _finds_by_type(typ):
+            fnc = anyconfig.processors.finds_with_pred
+            return fnc(lambda p: typ == p.type(), self.psrs)
 
-    def test_10_find_loader__w_parser_type_or_instance_or_by_file(self):
         cpath = "dummy.conf"
-        for psr in anyconfig.backends.Parsers().list():
-            self._assert_isinstance(TT.find_loader(cpath, psr.type()), psr)
-            self._assert_isinstance(TT.find_loader(cpath, psr()), psr)
+        for psr in self.psrs:
+            ldrs = _finds_by_type(psr.type())
+            self._assert_isinstances(TT.find_loader(cpath, psr.type()), ldrs)
+            self._assert_isinstances(TT.find_loader(cpath, psr()), ldrs)
+
+    def test_20_find_loader__w_parser_by_file(self):
+        def _find_ldrs_by_ext(ext):
+            fnc = anyconfig.processors.finds_with_pred
+            return fnc(lambda p: ext in p.extensions(), self.psrs)
+
+        for psr in self.psrs:
             for ext in psr.extensions():
-                self._assert_isinstance(TT.find_loader("dummy." + ext), psr,
-                                        "ext=%s, psr=%r" % (ext, psr))
+                ldrs = _find_ldrs_by_ext(ext)
+                self._assert_isinstances(TT.find_loader("dummy." + ext), ldrs)
 
     def test_30_find_loader__unknown_parser_type(self):
         self.assertRaises(TT.UnknownProcessorTypeError,