changeset 39788:ae531f5e583c

testing: add interface unit tests for file storage

Our strategy for supporting alternate storage backends is to define
interfaces for everything then "code to the interface."

We already have interfaces for various primitives, including file
and manifest storage.

What we don't have is generic unit tests for those interfaces. Up
to this point we've been relying on high-level integration tests
(mainly in the form of existing .t tests) to test alternate storage
backends. And my experience with developing the "simple store" test
extension is that such testing is very tedious: it takes several
minutes to run all tests and when you find a failure, it is often
non-trivial to debug.

This commit starts to change that.

This commit introduces the mercurial.testing.storage module. It
contains testing code for storage. Currently, it defines some
unittest.TestCase classes for testing the file storage interfaces.
It also defines some factory functions that allow a caller to easily
spawn a custom TestCase "bound" to a specific file storage backend
implementation.

A new .py test has been added. It simply defines a callable to produce
filelog and transaction instances on demand and then "registers" the
various test classes so the filelog class can be tested with the
storage interface unit tests.

As part of writing the tests, I identified a couple of apparent
bugs in revlog.py and filelog.py! These are tracked with inline
TODO comments.

Writing the tests makes it more obvious where the storage interface
is lacking. For example, we raise either IndexError or
error.LookupError for missing revisions depending on whether we
use an integer revision or a node. Also, we raise error.RevlogError
in various places when we should be raising a storage-agnostic
error type.

The storage interfaces are currently far from perfect and there is much
work to be done to improve them. But at least with this commit we
finally have the start of unit tests that can be used to "qualify"
the behavior of a storage backend. And when implementing and debugging
new storage backends, we now have an obvious place to define new
tests and have obvious places to insert breakpoints to facilitate
debugging. This should be invaluable when implementing new storage
backends.

I added the mercurial.testing package because these interface
conformance tests are generic and need to be usable by all storage
backends. Having the code live in tests/ would make it difficult for
storage backends implemented in extensions to test their interface
conformance. First, it would require obtaining a copy of Mercurial's
storage test code in order to test. Second, it would make testing
against multiple Mercurial versions difficult, as you would need to
import N copies of the storage testing code in order to achieve test
coverage. By making the test code part of the Mercurial distribution
itself, extensions can `import mercurial.testing.*` to access and run
the test code. The test will run against whatever Mercurial version
is active.

FWIW I've always wanted to move parts of run-tests.py into the
mercurial.* package to make the testing story simpler (e.g. imagine an
`hg debugruntests` command that could invoke the test harness). While I
have no plans to do that in the near future, establishing the
mercurial.testing package does provide a natural home for that code
should someone do this in the future.

Differential Revision: https://phab.mercurial-scm.org/D4650

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/testing/storage.py	Tue Sep 18 16:52:11 2018 -0700
@@ -0,0 +1,984 @@
+# storage.py - Testing of storage primitives.
+#
+# Copyright 2018 Gregory Szorc <[e-mail]>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+import unittest
+
+from ..node import (
+    hex,
+    nullid,
+    nullrev,
+)
+from .. import (
+    error,
+    mdiff,
+    revlog,
+)
+
+class basetestcase(unittest.TestCase):
+    if not getattr(unittest.TestCase, r'assertRaisesRegex', False):
+        assertRaisesRegex = (# camelcase-required
+            unittest.TestCase.assertRaisesRegexp)
+
+class revisiondeltarequest(object):
+    def __init__(self, node, p1, p2, linknode, basenode, ellipsis):
+        self.node = node
+        self.p1node = p1
+        self.p2node = p2
+        self.linknode = linknode
+        self.basenode = basenode
+        self.ellipsis = ellipsis
+
+class ifileindextests(basetestcase):
+    """Generic tests for the ifileindex interface.
+
+    All file storage backends for index data should conform to the tests in this
+    class.
+
+    Use ``makeifileindextests()`` to create an instance of this type.
+    """
+    def testempty(self):
+        f = self._makefilefn()
+        self.assertEqual(len(f), 0, 'new file store has 0 length by default')
+        self.assertEqual(list(f), [], 'iter yields nothing by default')
+
+        gen = iter(f)
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+        # revs() should evaluate to an empty list.
+        self.assertEqual(list(f.revs()), [])
+
+        revs = iter(f.revs())
+        with self.assertRaises(StopIteration):
+            next(revs)
+
+        self.assertEqual(list(f.revs(start=20)), [])
+
+        # parents() and parentrevs() work with nullid/nullrev.
+        self.assertEqual(f.parents(nullid), (nullid, nullid))
+        self.assertEqual(f.parentrevs(nullrev), (nullrev, nullrev))
+
+        with self.assertRaises(error.LookupError):
+            f.parents(b'\x01' * 20)
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.parentrevs(i)
+
+        # nullid/nullrev lookup always works.
+        self.assertEqual(f.rev(nullid), nullrev)
+        self.assertEqual(f.node(nullrev), nullid)
+
+        with self.assertRaises(error.LookupError):
+            f.rev(b'\x01' * 20)
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.node(i)
+
+        self.assertEqual(f.lookup(nullid), nullid)
+        self.assertEqual(f.lookup(nullrev), nullid)
+        self.assertEqual(f.lookup(hex(nullid)), nullid)
+
+        # String converted to integer doesn't work for nullrev.
+        with self.assertRaises(error.LookupError):
+            f.lookup(b'%d' % nullrev)
+
+        self.assertEqual(f.linkrev(nullrev), nullrev)
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.linkrev(i)
+
+        self.assertEqual(f.flags(nullrev), 0)
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.flags(i)
+
+        self.assertFalse(f.iscensored(nullrev))
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.iscensored(i)
+
+        self.assertEqual(list(f.commonancestorsheads(nullid, nullid)), [])
+
+        with self.assertRaises(ValueError):
+            self.assertEqual(list(f.descendants([])), [])
+
+        self.assertEqual(list(f.descendants([nullrev])), [])
+
+        self.assertEqual(f.headrevs(), [nullrev])
+        self.assertEqual(f.heads(), [nullid])
+        self.assertEqual(f.heads(nullid), [nullid])
+        self.assertEqual(f.heads(None, [nullid]), [nullid])
+        self.assertEqual(f.heads(nullid, [nullid]), [nullid])
+
+        self.assertEqual(f.children(nullid), [])
+
+        with self.assertRaises(error.LookupError):
+            f.children(b'\x01' * 20)
+
+        self.assertEqual(f.deltaparent(nullrev), nullrev)
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.deltaparent(i)
+
+    def testsinglerevision(self):
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            node = f.add(b'initial', None, tr, 0, nullid, nullid)
+
+        self.assertEqual(len(f), 1)
+        self.assertEqual(list(f), [0])
+
+        gen = iter(f)
+        self.assertEqual(next(gen), 0)
+
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+        self.assertEqual(list(f.revs()), [0])
+        self.assertEqual(list(f.revs(start=1)), [])
+        self.assertEqual(list(f.revs(start=0)), [0])
+        self.assertEqual(list(f.revs(stop=0)), [0])
+        self.assertEqual(list(f.revs(stop=1)), [0])
+        self.assertEqual(list(f.revs(1, 1)), [])
+        # TODO buggy
+        self.assertEqual(list(f.revs(1, 0)), [1, 0])
+        self.assertEqual(list(f.revs(2, 0)), [2, 1, 0])
+
+        self.assertEqual(f.parents(node), (nullid, nullid))
+        self.assertEqual(f.parentrevs(0), (nullrev, nullrev))
+
+        with self.assertRaises(error.LookupError):
+            f.parents(b'\x01' * 20)
+
+        with self.assertRaises(IndexError):
+            f.parentrevs(1)
+
+        self.assertEqual(f.rev(node), 0)
+
+        with self.assertRaises(error.LookupError):
+            f.rev(b'\x01' * 20)
+
+        self.assertEqual(f.node(0), node)
+
+        with self.assertRaises(IndexError):
+            f.node(1)
+
+        self.assertEqual(f.lookup(node), node)
+        self.assertEqual(f.lookup(0), node)
+        self.assertEqual(f.lookup(b'0'), node)
+        self.assertEqual(f.lookup(hex(node)), node)
+
+        self.assertEqual(f.linkrev(0), 0)
+
+        with self.assertRaises(IndexError):
+            f.linkrev(1)
+
+        self.assertEqual(f.flags(0), 0)
+
+        with self.assertRaises(IndexError):
+            f.flags(1)
+
+        self.assertFalse(f.iscensored(0))
+
+        with self.assertRaises(IndexError):
+            f.iscensored(1)
+
+        self.assertEqual(list(f.descendants([0])), [])
+
+        self.assertEqual(f.headrevs(), [0])
+
+        self.assertEqual(f.heads(), [node])
+        self.assertEqual(f.heads(node), [node])
+        self.assertEqual(f.heads(stop=[node]), [node])
+
+        with self.assertRaises(error.LookupError):
+            f.heads(stop=[b'\x01' * 20])
+
+        self.assertEqual(f.children(node), [])
+
+        self.assertEqual(f.deltaparent(0), nullrev)
+
+    def testmultiplerevisions(self):
+        fulltext0 = b'x' * 1024
+        fulltext1 = fulltext0 + b'y'
+        fulltext2 = b'y' + fulltext0 + b'z'
+
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            node0 = f.add(fulltext0, None, tr, 0, nullid, nullid)
+            node1 = f.add(fulltext1, None, tr, 1, node0, nullid)
+            node2 = f.add(fulltext2, None, tr, 3, node1, nullid)
+
+        self.assertEqual(len(f), 3)
+        self.assertEqual(list(f), [0, 1, 2])
+
+        gen = iter(f)
+        self.assertEqual(next(gen), 0)
+        self.assertEqual(next(gen), 1)
+        self.assertEqual(next(gen), 2)
+
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+        self.assertEqual(list(f.revs()), [0, 1, 2])
+        self.assertEqual(list(f.revs(0)), [0, 1, 2])
+        self.assertEqual(list(f.revs(1)), [1, 2])
+        self.assertEqual(list(f.revs(2)), [2])
+        self.assertEqual(list(f.revs(3)), [])
+        self.assertEqual(list(f.revs(stop=1)), [0, 1])
+        self.assertEqual(list(f.revs(stop=2)), [0, 1, 2])
+        self.assertEqual(list(f.revs(stop=3)), [0, 1, 2])
+        self.assertEqual(list(f.revs(2, 0)), [2, 1, 0])
+        self.assertEqual(list(f.revs(2, 1)), [2, 1])
+        # TODO this is wrong
+        self.assertEqual(list(f.revs(3, 2)), [3, 2])
+
+        self.assertEqual(f.parents(node0), (nullid, nullid))
+        self.assertEqual(f.parents(node1), (node0, nullid))
+        self.assertEqual(f.parents(node2), (node1, nullid))
+
+        self.assertEqual(f.parentrevs(0), (nullrev, nullrev))
+        self.assertEqual(f.parentrevs(1), (0, nullrev))
+        self.assertEqual(f.parentrevs(2), (1, nullrev))
+
+        self.assertEqual(f.rev(node0), 0)
+        self.assertEqual(f.rev(node1), 1)
+        self.assertEqual(f.rev(node2), 2)
+
+        with self.assertRaises(error.LookupError):
+            f.rev(b'\x01' * 20)
+
+        self.assertEqual(f.node(0), node0)
+        self.assertEqual(f.node(1), node1)
+        self.assertEqual(f.node(2), node2)
+
+        with self.assertRaises(IndexError):
+            f.node(3)
+
+        self.assertEqual(f.lookup(node0), node0)
+        self.assertEqual(f.lookup(0), node0)
+        self.assertEqual(f.lookup(b'0'), node0)
+        self.assertEqual(f.lookup(hex(node0)), node0)
+
+        self.assertEqual(f.lookup(node1), node1)
+        self.assertEqual(f.lookup(1), node1)
+        self.assertEqual(f.lookup(b'1'), node1)
+        self.assertEqual(f.lookup(hex(node1)), node1)
+
+        self.assertEqual(f.linkrev(0), 0)
+        self.assertEqual(f.linkrev(1), 1)
+        self.assertEqual(f.linkrev(2), 3)
+
+        with self.assertRaises(IndexError):
+            f.linkrev(3)
+
+        self.assertEqual(f.flags(0), 0)
+        self.assertEqual(f.flags(1), 0)
+        self.assertEqual(f.flags(2), 0)
+
+        with self.assertRaises(IndexError):
+            f.flags(3)
+
+        self.assertFalse(f.iscensored(0))
+        self.assertFalse(f.iscensored(1))
+        self.assertFalse(f.iscensored(2))
+
+        with self.assertRaises(IndexError):
+            f.iscensored(3)
+
+        self.assertEqual(f.commonancestorsheads(node1, nullid), [])
+        self.assertEqual(f.commonancestorsheads(node1, node0), [node0])
+        self.assertEqual(f.commonancestorsheads(node1, node1), [node1])
+        self.assertEqual(f.commonancestorsheads(node0, node1), [node0])
+        self.assertEqual(f.commonancestorsheads(node1, node2), [node1])
+        self.assertEqual(f.commonancestorsheads(node2, node1), [node1])
+
+        self.assertEqual(list(f.descendants([0])), [1, 2])
+        self.assertEqual(list(f.descendants([1])), [2])
+        self.assertEqual(list(f.descendants([0, 1])), [1, 2])
+
+        self.assertEqual(f.headrevs(), [2])
+
+        self.assertEqual(f.heads(), [node2])
+        self.assertEqual(f.heads(node0), [node2])
+        self.assertEqual(f.heads(node1), [node2])
+        self.assertEqual(f.heads(node2), [node2])
+
+        # TODO this behavior seems wonky. Is it correct? If so, the
+        # docstring for heads() should be updated to reflect desired
+        # behavior.
+        self.assertEqual(f.heads(stop=[node1]), [node1, node2])
+        self.assertEqual(f.heads(stop=[node0]), [node0, node2])
+        self.assertEqual(f.heads(stop=[node1, node2]), [node1, node2])
+
+        with self.assertRaises(error.LookupError):
+            f.heads(stop=[b'\x01' * 20])
+
+        self.assertEqual(f.children(node0), [node1])
+        self.assertEqual(f.children(node1), [node2])
+        self.assertEqual(f.children(node2), [])
+
+        self.assertEqual(f.deltaparent(0), nullrev)
+        self.assertEqual(f.deltaparent(1), 0)
+        self.assertEqual(f.deltaparent(2), 1)
+
+    def testmultipleheads(self):
+        f = self._makefilefn()
+
+        with self._maketransactionfn() as tr:
+            node0 = f.add(b'0', None, tr, 0, nullid, nullid)
+            node1 = f.add(b'1', None, tr, 1, node0, nullid)
+            node2 = f.add(b'2', None, tr, 2, node1, nullid)
+            node3 = f.add(b'3', None, tr, 3, node0, nullid)
+            node4 = f.add(b'4', None, tr, 4, node3, nullid)
+            node5 = f.add(b'5', None, tr, 5, node0, nullid)
+
+        self.assertEqual(len(f), 6)
+
+        self.assertEqual(list(f.descendants([0])), [1, 2, 3, 4, 5])
+        self.assertEqual(list(f.descendants([1])), [2])
+        self.assertEqual(list(f.descendants([2])), [])
+        self.assertEqual(list(f.descendants([3])), [4])
+        self.assertEqual(list(f.descendants([0, 1])), [1, 2, 3, 4, 5])
+        self.assertEqual(list(f.descendants([1, 3])), [2, 4])
+
+        self.assertEqual(f.headrevs(), [2, 4, 5])
+
+        self.assertEqual(f.heads(), [node2, node4, node5])
+        self.assertEqual(f.heads(node0), [node2, node4, node5])
+        self.assertEqual(f.heads(node1), [node2])
+        self.assertEqual(f.heads(node2), [node2])
+        self.assertEqual(f.heads(node3), [node4])
+        self.assertEqual(f.heads(node4), [node4])
+        self.assertEqual(f.heads(node5), [node5])
+
+        # TODO this seems wrong.
+        self.assertEqual(f.heads(stop=[node0]), [node0, node2, node4, node5])
+        self.assertEqual(f.heads(stop=[node1]), [node1, node2, node4, node5])
+
+        self.assertEqual(f.children(node0), [node1, node3, node5])
+        self.assertEqual(f.children(node1), [node2])
+        self.assertEqual(f.children(node2), [])
+        self.assertEqual(f.children(node3), [node4])
+        self.assertEqual(f.children(node4), [])
+        self.assertEqual(f.children(node5), [])
+
+class ifiledatatests(basetestcase):
+    """Generic tests for the ifiledata interface.
+
+    All file storage backends for data should conform to the tests in this
+    class.
+
+    Use ``makeifiledatatests()`` to create an instance of this type.
+    """
+    def testempty(self):
+        f = self._makefilefn()
+
+        self.assertEqual(f.rawsize(nullrev), 0)
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.rawsize(i)
+
+        self.assertEqual(f.size(nullrev), 0)
+
+        for i in range(-5, 5):
+            if i == nullrev:
+                continue
+
+            with self.assertRaises(IndexError):
+                f.size(i)
+
+        with self.assertRaises(error.RevlogError):
+            f.checkhash(b'', nullid)
+
+        with self.assertRaises(error.LookupError):
+            f.checkhash(b'', b'\x01' * 20)
+
+        self.assertEqual(f.revision(nullid), b'')
+        self.assertEqual(f.revision(nullid, raw=True), b'')
+
+        with self.assertRaises(error.LookupError):
+            f.revision(b'\x01' * 20)
+
+        self.assertEqual(f.read(nullid), b'')
+
+        with self.assertRaises(error.LookupError):
+            f.read(b'\x01' * 20)
+
+        self.assertFalse(f.renamed(nullid))
+
+        with self.assertRaises(error.LookupError):
+            f.read(b'\x01' * 20)
+
+        self.assertTrue(f.cmp(nullid, b''))
+        self.assertTrue(f.cmp(nullid, b'foo'))
+
+        with self.assertRaises(error.LookupError):
+            f.cmp(b'\x01' * 20, b'irrelevant')
+
+        self.assertEqual(f.revdiff(nullrev, nullrev), b'')
+
+        with self.assertRaises(IndexError):
+            f.revdiff(0, nullrev)
+
+        with self.assertRaises(IndexError):
+            f.revdiff(nullrev, 0)
+
+        with self.assertRaises(IndexError):
+            f.revdiff(0, 0)
+
+        gen = f.emitrevisiondeltas([])
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+        requests = [
+            revisiondeltarequest(nullid, nullid, nullid, nullid, nullid, False),
+        ]
+        gen = f.emitrevisiondeltas(requests)
+
+        delta = next(gen)
+
+        self.assertEqual(delta.node, nullid)
+        self.assertEqual(delta.p1node, nullid)
+        self.assertEqual(delta.p2node, nullid)
+        self.assertEqual(delta.linknode, nullid)
+        self.assertEqual(delta.basenode, nullid)
+        self.assertIsNone(delta.baserevisionsize)
+        self.assertEqual(delta.revision, b'')
+        self.assertIsNone(delta.delta)
+
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+        requests = [
+            revisiondeltarequest(nullid, nullid, nullid, nullid, nullid, False),
+            revisiondeltarequest(nullid, b'\x01' * 20, b'\x02' * 20,
+                                 b'\x03' * 20, nullid, False)
+        ]
+
+        gen = f.emitrevisiondeltas(requests)
+
+        next(gen)
+        delta = next(gen)
+
+        self.assertEqual(delta.node, nullid)
+        self.assertEqual(delta.p1node, b'\x01' * 20)
+        self.assertEqual(delta.p2node, b'\x02' * 20)
+        self.assertEqual(delta.linknode, b'\x03' * 20)
+        self.assertEqual(delta.basenode, nullid)
+        self.assertIsNone(delta.baserevisionsize)
+        self.assertEqual(delta.revision, b'')
+        self.assertIsNone(delta.delta)
+
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+    def testsinglerevision(self):
+        fulltext = b'initial'
+
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            node = f.add(fulltext, None, tr, 0, nullid, nullid)
+
+        self.assertEqual(f.rawsize(0), len(fulltext))
+
+        with self.assertRaises(IndexError):
+            f.rawsize(1)
+
+        self.assertEqual(f.size(0), len(fulltext))
+
+        with self.assertRaises(IndexError):
+            f.size(1)
+
+        f.checkhash(fulltext, node)
+        f.checkhash(fulltext, node, nullid, nullid)
+
+        with self.assertRaises(error.RevlogError):
+            f.checkhash(fulltext + b'extra', node)
+
+        with self.assertRaises(error.RevlogError):
+            f.checkhash(fulltext, node, b'\x01' * 20, nullid)
+
+        with self.assertRaises(error.RevlogError):
+            f.checkhash(fulltext, node, nullid, b'\x01' * 20)
+
+        self.assertEqual(f.revision(node), fulltext)
+        self.assertEqual(f.revision(node, raw=True), fulltext)
+
+        self.assertEqual(f.read(node), fulltext)
+
+        self.assertFalse(f.renamed(node))
+
+        self.assertFalse(f.cmp(node, fulltext))
+        self.assertTrue(f.cmp(node, fulltext + b'extra'))
+
+        self.assertEqual(f.revdiff(0, 0), b'')
+        self.assertEqual(f.revdiff(nullrev, 0),
+                         b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x07%s' %
+                         fulltext)
+
+        self.assertEqual(f.revdiff(0, nullrev),
+                         b'\x00\x00\x00\x00\x00\x00\x00\x07\x00\x00\x00\x00')
+
+        requests = [
+            revisiondeltarequest(node, nullid, nullid, nullid, nullid, False),
+        ]
+        gen = f.emitrevisiondeltas(requests)
+
+        delta = next(gen)
+
+        self.assertEqual(delta.node, node)
+        self.assertEqual(delta.p1node, nullid)
+        self.assertEqual(delta.p2node, nullid)
+        self.assertEqual(delta.linknode, nullid)
+        self.assertEqual(delta.basenode, nullid)
+        self.assertIsNone(delta.baserevisionsize)
+        self.assertEqual(delta.revision, fulltext)
+        self.assertIsNone(delta.delta)
+
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+    def testmultiplerevisions(self):
+        fulltext0 = b'x' * 1024
+        fulltext1 = fulltext0 + b'y'
+        fulltext2 = b'y' + fulltext0 + b'z'
+
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            node0 = f.add(fulltext0, None, tr, 0, nullid, nullid)
+            node1 = f.add(fulltext1, None, tr, 1, node0, nullid)
+            node2 = f.add(fulltext2, None, tr, 3, node1, nullid)
+
+        self.assertEqual(f.rawsize(0), len(fulltext0))
+        self.assertEqual(f.rawsize(1), len(fulltext1))
+        self.assertEqual(f.rawsize(2), len(fulltext2))
+
+        with self.assertRaises(IndexError):
+            f.rawsize(3)
+
+        self.assertEqual(f.size(0), len(fulltext0))
+        self.assertEqual(f.size(1), len(fulltext1))
+        self.assertEqual(f.size(2), len(fulltext2))
+
+        with self.assertRaises(IndexError):
+            f.size(3)
+
+        f.checkhash(fulltext0, node0)
+        f.checkhash(fulltext1, node1)
+        f.checkhash(fulltext1, node1, node0, nullid)
+        f.checkhash(fulltext2, node2, node1, nullid)
+
+        with self.assertRaises(error.RevlogError):
+            f.checkhash(fulltext1, b'\x01' * 20)
+
+        with self.assertRaises(error.RevlogError):
+            f.checkhash(fulltext1 + b'extra', node1, node0, nullid)
+
+        with self.assertRaises(error.RevlogError):
+            f.checkhash(fulltext1, node1, node0, node0)
+
+        self.assertEqual(f.revision(node0), fulltext0)
+        self.assertEqual(f.revision(node0, raw=True), fulltext0)
+        self.assertEqual(f.revision(node1), fulltext1)
+        self.assertEqual(f.revision(node1, raw=True), fulltext1)
+        self.assertEqual(f.revision(node2), fulltext2)
+        self.assertEqual(f.revision(node2, raw=True), fulltext2)
+
+        with self.assertRaises(error.LookupError):
+            f.revision(b'\x01' * 20)
+
+        self.assertEqual(f.read(node0), fulltext0)
+        self.assertEqual(f.read(node1), fulltext1)
+        self.assertEqual(f.read(node2), fulltext2)
+
+        with self.assertRaises(error.LookupError):
+            f.read(b'\x01' * 20)
+
+        self.assertFalse(f.renamed(node0))
+        self.assertFalse(f.renamed(node1))
+        self.assertFalse(f.renamed(node2))
+
+        with self.assertRaises(error.LookupError):
+            f.renamed(b'\x01' * 20)
+
+        self.assertFalse(f.cmp(node0, fulltext0))
+        self.assertFalse(f.cmp(node1, fulltext1))
+        self.assertFalse(f.cmp(node2, fulltext2))
+
+        self.assertTrue(f.cmp(node1, fulltext0))
+        self.assertTrue(f.cmp(node2, fulltext1))
+
+        with self.assertRaises(error.LookupError):
+            f.cmp(b'\x01' * 20, b'irrelevant')
+
+        self.assertEqual(f.revdiff(0, 1),
+                         b'\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x04\x01' +
+                         fulltext1)
+
+        self.assertEqual(f.revdiff(0, 2),
+                         b'\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x04\x02' +
+                         fulltext2)
+
+        requests = [
+            revisiondeltarequest(node0, nullid, nullid, b'\x01' * 20, nullid,
+                                 False),
+            revisiondeltarequest(node1, node0, nullid, b'\x02' * 20, node0,
+                                 False),
+            revisiondeltarequest(node2, node1, nullid, b'\x03' * 20, node1,
+                                 False),
+        ]
+        gen = f.emitrevisiondeltas(requests)
+
+        delta = next(gen)
+
+        self.assertEqual(delta.node, node0)
+        self.assertEqual(delta.p1node, nullid)
+        self.assertEqual(delta.p2node, nullid)
+        self.assertEqual(delta.linknode, b'\x01' * 20)
+        self.assertEqual(delta.basenode, nullid)
+        self.assertIsNone(delta.baserevisionsize)
+        self.assertEqual(delta.revision, fulltext0)
+        self.assertIsNone(delta.delta)
+
+        delta = next(gen)
+
+        self.assertEqual(delta.node, node1)
+        self.assertEqual(delta.p1node, node0)
+        self.assertEqual(delta.p2node, nullid)
+        self.assertEqual(delta.linknode, b'\x02' * 20)
+        self.assertEqual(delta.basenode, node0)
+        self.assertIsNone(delta.baserevisionsize)
+        self.assertIsNone(delta.revision)
+        self.assertEqual(delta.delta,
+                         b'\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x04\x01' +
+                         fulltext1)
+
+        delta = next(gen)
+
+        self.assertEqual(delta.node, node2)
+        self.assertEqual(delta.p1node, node1)
+        self.assertEqual(delta.p2node, nullid)
+        self.assertEqual(delta.linknode, b'\x03' * 20)
+        self.assertEqual(delta.basenode, node1)
+        self.assertIsNone(delta.baserevisionsize)
+        self.assertIsNone(delta.revision)
+        self.assertEqual(delta.delta,
+                         b'\x00\x00\x00\x00\x00\x00\x04\x01\x00\x00\x04\x02' +
+                         fulltext2)
+
+        with self.assertRaises(StopIteration):
+            next(gen)
+
+    def testrenamed(self):
+        fulltext0 = b'foo'
+        fulltext1 = b'bar'
+        fulltext2 = b'baz'
+
+        meta1 = {
+            b'copy': b'source0',
+            b'copyrev': b'a' * 40,
+        }
+
+        meta2 = {
+            b'copy': b'source1',
+            b'copyrev': b'b' * 40,
+        }
+
+        stored1 = b''.join([
+            b'\x01\ncopy: source0\n',
+            b'copyrev: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n\x01\n',
+            fulltext1,
+        ])
+
+        stored2 = b''.join([
+            b'\x01\ncopy: source1\n',
+            b'copyrev: bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\n\x01\n',
+            fulltext2,
+        ])
+
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            node0 = f.add(fulltext0, None, tr, 0, nullid, nullid)
+            node1 = f.add(fulltext1, meta1, tr, 1, node0, nullid)
+            node2 = f.add(fulltext2, meta2, tr, 2, nullid, nullid)
+
+        self.assertEqual(f.rawsize(1), len(stored1))
+        self.assertEqual(f.rawsize(2), len(stored2))
+
+        # Metadata header isn't recognized when parent isn't nullid.
+        self.assertEqual(f.size(1), len(stored1))
+        self.assertEqual(f.size(2), len(fulltext2))
+
+        self.assertEqual(f.revision(node1), stored1)
+        self.assertEqual(f.revision(node1, raw=True), stored1)
+        self.assertEqual(f.revision(node2), stored2)
+        self.assertEqual(f.revision(node2, raw=True), stored2)
+
+        self.assertEqual(f.read(node1), fulltext1)
+        self.assertEqual(f.read(node2), fulltext2)
+
+        # Returns False when first parent is set.
+        self.assertFalse(f.renamed(node1))
+        self.assertEqual(f.renamed(node2), (b'source1', b'\xbb' * 20))
+
+        self.assertTrue(f.cmp(node1, fulltext1))
+        self.assertTrue(f.cmp(node1, stored1))
+        self.assertFalse(f.cmp(node2, fulltext2))
+        self.assertTrue(f.cmp(node2, stored2))
+
+    def testmetadataprefix(self):
+        # Content with metadata prefix has extra prefix inserted in storage.
+        fulltext0 = b'\x01\nfoo'
+        stored0 = b'\x01\n\x01\n\x01\nfoo'
+
+        fulltext1 = b'\x01\nbar'
+        meta1 = {
+            b'copy': b'source0',
+            b'copyrev': b'b' * 40,
+        }
+        stored1 = b''.join([
+            b'\x01\ncopy: source0\n',
+            b'copyrev: %s\n' % (b'b' * 40),
+            b'\x01\n\x01\nbar',
+        ])
+
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            node0 = f.add(fulltext0, {}, tr, 0, nullid, nullid)
+            node1 = f.add(fulltext1, meta1, tr, 1, nullid, nullid)
+
+        self.assertEqual(f.rawsize(0), len(stored0))
+        self.assertEqual(f.rawsize(1), len(stored1))
+
+        # TODO this is buggy.
+        self.assertEqual(f.size(0), len(fulltext0) + 4)
+
+        self.assertEqual(f.size(1), len(fulltext1))
+
+        self.assertEqual(f.revision(node0), stored0)
+        self.assertEqual(f.revision(node0, raw=True), stored0)
+
+        self.assertEqual(f.revision(node1), stored1)
+        self.assertEqual(f.revision(node1, raw=True), stored1)
+
+        self.assertEqual(f.read(node0), fulltext0)
+        self.assertEqual(f.read(node1), fulltext1)
+
+        self.assertFalse(f.cmp(node0, fulltext0))
+        self.assertTrue(f.cmp(node0, stored0))
+
+        self.assertFalse(f.cmp(node1, fulltext1))
+        self.assertTrue(f.cmp(node1, stored0))
+
+    def testcensored(self):
+        f = self._makefilefn()
+
+        stored1 = revlog.packmeta({
+            b'censored': b'tombstone',
+        }, b'')
+
+        # TODO tests are incomplete because we need the node to be
+        # different due to presence of censor metadata. But we can't
+        # do this with addrevision().
+        with self._maketransactionfn() as tr:
+            node0 = f.add(b'foo', None, tr, 0, nullid, nullid)
+            f.addrevision(stored1, tr, 1, node0, nullid,
+                          flags=revlog.REVIDX_ISCENSORED)
+
+        self.assertEqual(f.flags(1), revlog.REVIDX_ISCENSORED)
+        self.assertTrue(f.iscensored(1))
+
+        self.assertEqual(f.revision(1), stored1)
+        self.assertEqual(f.revision(1, raw=True), stored1)
+
+        self.assertEqual(f.read(1), b'')
+
+class ifilemutationtests(basetestcase):
+    """Generic tests for the ifilemutation interface.
+
+    All file storage backends that support writing should conform to this
+    interface.
+
+    Use ``makeifilemutationtests()`` to create an instance of this type.
+    """
+    def testaddnoop(self):
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            node0 = f.add(b'foo', None, tr, 0, nullid, nullid)
+            node1 = f.add(b'foo', None, tr, 0, nullid, nullid)
+            # Varying by linkrev shouldn't impact hash.
+            node2 = f.add(b'foo', None, tr, 1, nullid, nullid)
+
+        self.assertEqual(node1, node0)
+        self.assertEqual(node2, node0)
+        self.assertEqual(len(f), 1)
+
+    def testaddrevisionbadnode(self):
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            # Adding a revision with bad node value fails.
+            with self.assertRaises(error.RevlogError):
+                f.addrevision(b'foo', tr, 0, nullid, nullid, node=b'\x01' * 20)
+
+    def testaddrevisionunknownflag(self):
+        f = self._makefilefn()
+        with self._maketransactionfn() as tr:
+            for i in range(15, 0, -1):
+                if (1 << i) & ~revlog.REVIDX_KNOWN_FLAGS:
+                    flags = 1 << i
+                    break
+
+            with self.assertRaises(error.RevlogError):
+                f.addrevision(b'foo', tr, 0, nullid, nullid, flags=flags)
+
+    def testaddgroupsimple(self):
+        f = self._makefilefn()
+
+        callbackargs = []
+        def cb(*args, **kwargs):
+            callbackargs.append((args, kwargs))
+
+        def linkmapper(node):
+            return 0
+
+        with self._maketransactionfn() as tr:
+            nodes = f.addgroup([], None, tr, addrevisioncb=cb)
+
+        self.assertEqual(nodes, [])
+        self.assertEqual(callbackargs, [])
+        self.assertEqual(len(f), 0)
+
+        fulltext0 = b'foo'
+        delta0 = mdiff.trivialdiffheader(len(fulltext0)) + fulltext0
+
+        deltas = [
+            (b'\x01' * 20, nullid, nullid, nullid, nullid, delta0, 0),
+        ]
+
+        with self._maketransactionfn() as tr:
+            with self.assertRaises(error.RevlogError):
+                f.addgroup(deltas, linkmapper, tr, addrevisioncb=cb)
+
+            node0 = f.add(fulltext0, None, tr, 0, nullid, nullid)
+
+        f = self._makefilefn()
+
+        deltas = [
+            (node0, nullid, nullid, nullid, nullid, delta0, 0),
+        ]
+
+        with self._maketransactionfn() as tr:
+            nodes = f.addgroup(deltas, linkmapper, tr, addrevisioncb=cb)
+
+        self.assertEqual(nodes, [
+            b'\x49\xd8\xcb\xb1\x5c\xe2\x57\x92\x04\x47'
+            b'\x00\x6b\x46\x97\x8b\x7a\xf9\x80\xa9\x79'])
+
+        self.assertEqual(len(callbackargs), 1)
+        self.assertEqual(callbackargs[0][0][1], nodes[0])
+
+        self.assertEqual(list(f.revs()), [0])
+        self.assertEqual(f.rev(nodes[0]), 0)
+        self.assertEqual(f.node(0), nodes[0])
+
+    def testaddgroupmultiple(self):
+        f = self._makefilefn()
+
+        fulltexts = [
+            b'foo',
+            b'bar',
+            b'x' * 1024,
+        ]
+
+        nodes = []
+        with self._maketransactionfn() as tr:
+            for fulltext in fulltexts:
+                nodes.append(f.add(fulltext, None, tr, 0, nullid, nullid))
+
+        f = self._makefilefn()
+        deltas = []
+        for i, fulltext in enumerate(fulltexts):
+            delta = mdiff.trivialdiffheader(len(fulltext)) + fulltext
+
+            deltas.append((nodes[i], nullid, nullid, nullid, nullid, delta, 0))
+
+        with self._maketransactionfn() as tr:
+            self.assertEqual(f.addgroup(deltas, lambda x: 0, tr), nodes)
+
+        self.assertEqual(len(f), len(deltas))
+        self.assertEqual(list(f.revs()), [0, 1, 2])
+        self.assertEqual(f.rev(nodes[0]), 0)
+        self.assertEqual(f.rev(nodes[1]), 1)
+        self.assertEqual(f.rev(nodes[2]), 2)
+        self.assertEqual(f.node(0), nodes[0])
+        self.assertEqual(f.node(1), nodes[1])
+        self.assertEqual(f.node(2), nodes[2])
+
+def makeifileindextests(makefilefn, maketransactionfn):
+    """Create a unittest.TestCase class suitable for testing file storage.
+
+    ``makefilefn`` is a callable which receives the test case as an
+    argument and returns an object implementing the ``ifilestorage`` interface.
+
+    ``maketransactionfn`` is a callable which receives the test case as an
+    argument and returns a transaction object.
+
+    Returns a type that is a ``unittest.TestCase`` that can be used for
+    testing the object implementing the file storage interface. Simply
+    assign the returned value to a module-level attribute and a test loader
+    should find and run it automatically.
+    """
+    d = {
+        r'_makefilefn': makefilefn,
+        r'_maketransactionfn': maketransactionfn,
+    }
+    return type(r'ifileindextests', (ifileindextests,), d)
+
+def makeifiledatatests(makefilefn, maketransactionfn):
+    d = {
+        r'_makefilefn': makefilefn,
+        r'_maketransactionfn': maketransactionfn,
+    }
+    return type(r'ifiledatatests', (ifiledatatests,), d)
+
+def makeifilemutationtests(makefilefn, maketransactionfn):
+    d = {
+        r'_makefilefn': makefilefn,
+        r'_maketransactionfn': maketransactionfn,
+    }
+    return type(r'ifilemutationtests', (ifilemutationtests,), d)

--- a/setup.py	Tue Sep 18 15:32:11 2018 -0700
+++ b/setup.py	Tue Sep 18 16:52:11 2018 -0700
@@ -822,6 +822,7 @@
             'mercurial.thirdparty.zope.interface',
             'mercurial.utils',
             'mercurial.revlogutils',
+            'mercurial.testing',
             'hgext', 'hgext.convert', 'hgext.fsmonitor',
             'hgext.fastannotate',
             'hgext.fsmonitor.pywatchman',

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-storage.py	Tue Sep 18 16:52:11 2018 -0700
@@ -0,0 +1,46 @@
+# This test verifies the conformance of various classes to various
+# storage interfaces.
+from __future__ import absolute_import
+
+import silenttestrunner
+
+from mercurial import (
+    filelog,
+    transaction,
+    ui as uimod,
+    vfs as vfsmod,
+)
+
+from mercurial.testing import (
+    storage as storagetesting,
+)
+
+STATE = {
+    'lastindex': 0,
+    'ui': uimod.ui(),
+    'vfs': vfsmod.vfs(b'.', realpath=True),
+}
+
+def makefilefn(self):
+    """Factory for filelog instances."""
+    fl = filelog.filelog(STATE['vfs'], 'filelog-%d' % STATE['lastindex'])
+    STATE['lastindex'] += 1
+    return fl
+
+def maketransaction(self):
+    vfsmap = {'plain': STATE['vfs']}
+
+    return transaction.transaction(STATE['ui'].warn, STATE['vfs'], vfsmap,
+                                  'journal', 'undo')
+
+# Assigning module-level attributes that inherit from unittest.TestCase
+# is all that is needed to register tests.
+filelogindextests = storagetesting.makeifileindextests(makefilefn,
+                                                       maketransaction)
+filelogdatatests = storagetesting.makeifiledatatests(makefilefn,
+                                                     maketransaction)
+filelogmutationtests = storagetesting.makeifilemutationtests(makefilefn,
+                                                             maketransaction)
+
+if __name__ == '__main__':
+    silenttestrunner.main(__name__)