atomic dual-write tests

refactors so the FakeFile and Verifier classes can be used in multiple
tests and adds a helper function to verify data.

adds new tests similar to the previous atomic write tests, but this time
does a second write in the middle of writing (rather than doing a read
in the middle)

test_s3.py

@@ -1001,11 +1001,6 @@ def test_100_continue():
     status = _simple_http_req_100_cont(s3.main.host, s3.main.port, 'PUT', resource)
     eq(status, '100')
 
-def _test_atomic_write(file_size):
-    bucket = get_new_bucket()
-    objname = 'testobj'
-    key = bucket.new_key(objname)
-
 class FakeFile(object):
     def __init__(self, size, char='A', interrupt=None):
         self.offset = 0
@@ -1043,26 +1038,33 @@ def _test_atomic_write(file_size):
         self.size += size
         eq(data, self.char*size)
 
+def _verify_atomic_key_data(key, size=-1, char=None):
+    fp_verify = FakeFileVerifier(char)
+    key.get_contents_to_file(fp_verify)
+    if size >= 0:
+        eq(fp_verify.size, size)
+
+def _test_atomic_write(file_size):
+    bucket = get_new_bucket()
+    objname = 'testobj'
+    key = bucket.new_key(objname)
+
     # create <file_size> file of A's
     fp_a = FakeFile(file_size, 'A')
     key.set_contents_from_file(fp_a)
     
     # verify A's
-    fp_a_verify = FakeFileVerifier('A')
+    _verify_atomic_key_data(key, file_size, 'A')
-    key.get_contents_to_file(fp_a_verify)
-    eq(fp_a_verify.size, file_size)
 
     # create <file_size> file of B's
     # but try to verify the file before we finish writing all the B's
     fp_b = FakeFile(file_size, 'B',
-        lambda: key.get_contents_to_file(FakeFileVerifier())
+        lambda: _verify_atomic_key_data(key, file_size)
         )
     key.set_contents_from_file(fp_b)
 
     # verify B's
-    fp_b_verify = FakeFileVerifier('B')
+    _verify_atomic_key_data(key, file_size, 'B')
-    key.get_contents_to_file(fp_b_verify)
-    eq(fp_b_verify.size, file_size)
 
 def test_atomic_write_1mb():
     _test_atomic_write(1024*1024)
@@ -1073,3 +1075,31 @@ def test_atomic_write_4mb():
 def test_atomic_write_8mb():
     _test_atomic_write(1024*1024*8)
 
+def _test_atomic_dual_write(file_size):
+    bucket = get_new_bucket()
+    objname = 'testobj'
+    key = bucket.new_key(objname)
+    
+    # get a second key object (for the same key)
+    # so both can be writing without interfering
+    key2 = bucket.new_key(objname)
+
+    # write <file_size> file of B's
+    # but before we're done, try to write all A's
+    fp_a = FakeFile(file_size, 'A')
+    fp_b = FakeFile(file_size, 'B',
+        lambda: key2.set_contents_from_file(fp_a)
+        )
+    key.set_contents_from_file(fp_b)
+
+    # verify the file
+    _verify_atomic_key_data(key, file_size)
+
+def test_atomic_dual_write_1mb():
+    _test_atomic_dual_write(1024*1024)
+
+def test_atomic_dual_write_4mb():
+    _test_atomic_dual_write(1024*1024*4)
+
+def test_atomic_dual_write_8mb():
+    _test_atomic_dual_write(1024*1024*8)