refs: Added is_valid method to SymbolicReference base class

Author: Byron

lib/git/refs.py

@@ -214,6 +214,19 @@ def _set_reference(self, ref):
 	# alias
 	ref = reference
 
+	def is_valid(self):
+		"""
+		Returns
+			True if the reference is valid, hence it can be read and points to 
+			a valid object or reference.
+		"""
+		try:
+			self.commit
+		except (OSError, ValueError):
+			return False
+		else:
+			return True
+		
 	@property
 	def is_detached(self):
 		"""

test/git/test_refs.py

@@ -66,6 +66,12 @@ def test_refs(self):
 			types_found.add(type(ref))
 		assert len(types_found) == 3 
 
+	def test_is_valid(self):
+		assert Reference(self.rorepo, 'refs/doesnt/exist').is_valid() == False
+		assert self.rorepo.head.is_valid()
+		assert self.rorepo.head.reference.is_valid()
+		assert SymbolicReference(self.rorepo, 'hellothere').is_valid() == False
+		
 	@with_rw_repo('0.1.6')
 	def test_head_reset(self, rw_repo):
 		cur_head = rw_repo.head