diff --git a/tests/test-revlog-delta-find.t b/tests/test-revlog-delta-find.t
new file mode 100644
--- /dev/null
+++ b/tests/test-revlog-delta-find.t
@@ -0,0 +1,193 @@
+==========================================================
+Test various things around delta computation within revlog
+==========================================================
+
+
+basic setup
+-----------
+
+  $ cat << EOF >> $HGRCPATH
+  > [debug]
+  > revlog.debug-delta=yes
+  > EOF
+  $ cat << EOF >> sha256line.py
+  > # a way to quickly produce file of significant size and poorly compressable content.
+  > import hashlib
+  > import sys
+  > for line in sys.stdin:
+  >     print(hashlib.sha256(line.encode('utf8')).hexdigest())
+  > EOF
+
+  $ hg init base-repo
+  $ cd base-repo
+
+create a "large" file
+
+  $ $TESTDIR/seq.py 1000 | $PYTHON $TESTTMP/sha256line.py > my-file.txt
+  $ hg add my-file.txt
+  $ hg commit -m initial-commit
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+Add more change at the end of the file
+
+  $ $TESTDIR/seq.py 1001 1200 | $PYTHON $TESTTMP/sha256line.py >> my-file.txt
+  $ hg commit -m "large-change"
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+Add small change at the start
+
+  $ hg up 'desc("initial-commit")' --quiet
+  $ mv my-file.txt foo
+  $ echo "small change at the start" > my-file.txt
+  $ cat foo >> my-file.txt
+  $ rm foo
+  $ hg commit -m "small-change"
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  created new head
+
+
+  $ hg log -r 'head()' -T '{node}\n' >> ../base-heads.nodes
+  $ hg log -r 'desc("initial-commit")' -T '{node}\n' >> ../initial.node
+  $ hg log -r 'desc("small-change")' -T '{node}\n' >> ../small.node
+  $ hg log -r 'desc("large-change")' -T '{node}\n' >> ../large.node
+  $ cd ..
+
+Check delta find policy and result for merge on commit
+======================================================
+
+Check that delta of merge pick best of the two parents
+------------------------------------------------------
+
+As we check against both parents, the one with the largest change should
+produce the smallest delta and be picked.
+
+  $ hg clone base-repo test-parents --quiet
+  $ hg -R test-parents update 'nodefromfile("small.node")' --quiet
+  $ hg -R test-parents merge 'nodefromfile("large.node")' --quiet
+
+The delta base is the "large" revision as it produce a smaller delta.
+
+  $ hg -R test-parents commit -m "merge from small change"
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=1 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+Check that the behavior tested above can we disabled
+----------------------------------------------------
+
+We disable the checking of both parent at the same time. The `small` change,
+that produce a less optimal delta, should be picked first as it is "closer" to
+the new commit.
+
+  $ hg clone base-repo test-no-parents --quiet
+  $ hg -R test-no-parents update 'nodefromfile("small.node")' --quiet
+  $ hg -R test-no-parents merge 'nodefromfile("large.node")' --quiet
+
+The delta base is the "large" revision as it produce a smaller delta.
+
+  $ hg -R test-no-parents commit -m "merge from small change" \
+  > --config storage.revlog.optimize-delta-parent-choice=no
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=2 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+
+Check delta-find policy and result when unbundling
+==================================================
+
+Build a bundle with all delta built against p1
+
+  $ hg bundle -R test-parents --all --config devel.bundle.delta=p1 all-p1.hg
+  4 changesets found
+
+Default policy of trusting delta from the bundle
+------------------------------------------------
+
+Keeping the `p1` delta used in the bundle is sub-optimal for storage, but
+strusting in-bundle delta is faster to apply.
+
+  $ hg init bundle-default
+  $ hg -R bundle-default unbundle all-p1.hg --quiet
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=2 * (glob)
+
+(confirm the file revision are in the same order, 2 should be smaller than 1)
+
+  $ hg -R bundle-default debugdata my-file.txt 2 | wc -l
+  \s*1001 (re)
+  $ hg -R bundle-default debugdata my-file.txt 1 | wc -l
+  \s*1200 (re)
+
+explicitly enabled
+------------------
+
+Keeping the `p1` delta used in the bundle is sub-optimal for storage, but
+strusting in-bundle delta is faster to apply.
+
+  $ hg init bundle-reuse-enabled
+  $ hg -R bundle-reuse-enabled unbundle all-p1.hg --quiet \
+  > --config storage.revlog.reuse-external-delta-parent=yes
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=2 * (glob)
+
+(confirm the file revision are in the same order, 2 should be smaller than 1)
+
+  $ hg -R bundle-reuse-enabled debugdata my-file.txt 2 | wc -l
+  \s*1001 (re)
+  $ hg -R bundle-reuse-enabled debugdata my-file.txt 1 | wc -l
+  \s*1200 (re)
+
+explicitly disabled
+-------------------
+
+Not reusing the delta-base from the parent means we the delta will be made
+against the "best" parent. (so not the same as the previous two)
+
+  $ hg init bundle-reuse-disabled
+  $ hg -R bundle-reuse-disabled unbundle all-p1.hg --quiet \
+  > --config storage.revlog.reuse-external-delta-parent=no
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=1 * (glob)
+
+(confirm the file revision are in the same order, 2 should be smaller than 1)
+
+  $ hg -R bundle-reuse-disabled debugdata my-file.txt 2 | wc -l
+  \s*1001 (re)
+  $ hg -R bundle-reuse-disabled debugdata my-file.txt 1 | wc -l
+  \s*1200 (re)