diff --git a/tests/test-transaction-safety.t b/tests/test-transaction-safety.t
new file mode 100644
--- /dev/null
+++ b/tests/test-transaction-safety.t
@@ -0,0 +1,186 @@
+Test transaction safety
+=======================
+
+This test basic case to make sure external process do not see transaction
+content until it is committed.
+
+# TODO: also add an external reader accessing revlog files while they are written
+#       (instead of during transaction finalisation)
+
+# TODO: also add stream clone and hardlink clone happening during these transaction.
+
+setup
+-----
+
+synchronisation+output script:
+
+  $ mkdir sync
+  $ mkdir output
+  $ mkdir script
+  $ HG_TEST_FILE_EXT_WAITING=$TESTTMP/sync/ext_waiting
+  $ export HG_TEST_FILE_EXT_WAITING
+  $ HG_TEST_FILE_EXT_UNLOCK=$TESTTMP/sync/ext_unlock
+  $ export HG_TEST_FILE_EXT_UNLOCK
+  $ HG_TEST_FILE_EXT_DONE=$TESTTMP/sync/ext_done
+  $ export HG_TEST_FILE_EXT_DONE
+  $ cat << EOF > script/external.sh
+  > #!/bin/sh
+  > $RUNTESTDIR/testlib/wait-on-file 5 $HG_TEST_FILE_EXT_UNLOCK $HG_TEST_FILE_EXT_WAITING
+  > hg log --rev 'tip' -T 'external: {rev} {desc}\n' > $TESTTMP/output/external.out
+  > touch $HG_TEST_FILE_EXT_DONE
+  > EOF
+  $ chmod +x script/external.sh
+  $ cat << EOF > script/internal.sh
+  > #!/bin/sh
+  > hg log --rev 'tip' -T 'internal: {rev} {desc}\n' > $TESTTMP/output/internal.out
+  > $RUNTESTDIR/testlib/wait-on-file 5 $HG_TEST_FILE_EXT_DONE $HG_TEST_FILE_EXT_UNLOCK
+  > EOF
+  $ chmod +x script/internal.sh
+
+
+Automated commands:
+
+  $ make_one_commit() {
+  > rm -f $TESTTMP/sync/*
+  > rm -f $TESTTMP/output/*
+  > hg log --rev 'tip' -T 'pre-commit: {rev} {desc}\n'
+  > echo x >> a
+  > $TESTTMP/script/external.sh & hg commit -m "$1"
+  > cat $TESTTMP/output/external.out
+  > cat $TESTTMP/output/internal.out
+  > hg log --rev 'tip' -T 'post-tr:  {rev} {desc}\n'
+  > }
+
+
+  $ make_one_pull() {
+  > rm -f $TESTTMP/sync/*
+  > rm -f $TESTTMP/output/*
+  > hg log --rev 'tip' -T 'pre-commit: {rev} {desc}\n'
+  > echo x >> a
+  > $TESTTMP/script/external.sh & hg pull ../other-repo/ --rev "$1" --force --quiet
+  > cat $TESTTMP/output/external.out
+  > cat $TESTTMP/output/internal.out
+  > hg log --rev 'tip' -T 'post-tr:  {rev} {desc}\n'
+  > }
+
+prepare a large source to which to pull from:
+
+The source is large to unsure we don't use inline more after the pull
+
+  $ hg init other-repo
+  $ hg -R other-repo debugbuilddag .+500
+
+
+prepare an empty repository where to make test:
+
+  $ hg init repo
+  $ cd repo
+  $ touch a
+  $ hg add a
+
+prepare a small extension to controll inline size
+
+  $ mkdir $TESTTMP/ext
+  $ cat << EOF > $TESTTMP/ext/small_inline.py
+  > from mercurial import revlog
+  > revlog._maxinline = 64 * 100
+  > EOF
+
+
+
+
+  $ cat << EOF >> $HGRCPATH
+  > [extensions]
+  > small_inline=$TESTTMP/ext/small_inline.py
+  > [hooks]
+  > pretxnclose = $TESTTMP/script/internal.sh
+  > EOF
+
+check this is true for the initial commit (inline → inline)
+-----------------------------------------------------------
+
+the repository should still be inline (for relevant format)
+
+  $ make_one_commit first
+  pre-commit: -1 
+  external: -1 
+  internal: 0 first
+  post-tr:  0 first
+  $ hg debugrevlog -c | grep inline
+  flags  : inline
+
+check this is true for extra commit (inline → inline)
+-----------------------------------------------------
+
+the repository should still be inline (for relevant format)
+
+  $ hg debugrevlog -c | grep inline
+  flags  : inline
+  $ make_one_commit second
+  pre-commit: 0 first
+  external: 0 first
+  internal: 1 second
+  post-tr:  1 second
+  $ hg debugrevlog -c | grep inline
+  flags  : inline
+
+check this is true for a small pull (inline → inline)
+-----------------------------------------------------
+
+the repository should still be inline (for relevant format)
+
+  $ hg debugrevlog -c | grep inline
+  flags  : inline
+  $ make_one_pull 3
+  pre-commit: 1 second
+  warning: repository is unrelated
+  external: 1 second
+  internal: 5 r3
+  post-tr:  5 r3
+  $ hg debugrevlog -c | grep inline
+  flags  : inline
+
+Make a large pull (inline → no-inline)
+---------------------------------------
+
+the repository should no longer be inline (for relevant format)
+
+  $ hg debugrevlog -c | grep inline
+  flags  : inline
+  $ make_one_pull 400
+  pre-commit: 5 r3
+  external: 5 r3
+  internal: 402 r400
+  post-tr:  402 r400
+  $ hg debugrevlog -c | grep inline
+  [1]
+
+check this is true for extra commit (no-inline → no-inline)
+-----------------------------------------------------------
+
+the repository should no longer be inline (for relevant format)
+  $ hg debugrevlog -c | grep inline
+  [1]
+  $ make_one_commit third
+  pre-commit: 402 r400
+  external: 402 r400
+  internal: 403 third
+  post-tr:  403 third
+  $ hg debugrevlog -c | grep inline
+  [1]
+
+
+Make a  pull (not-inline → no-inline)
+-------------------------------------
+
+the repository should no longer be inline (for relevant format)
+
+  $ hg debugrevlog -c | grep inline
+  [1]
+  $ make_one_pull tip
+  pre-commit: 403 third
+  external: 403 third
+  internal: 503 r500
+  post-tr:  503 r500
+  $ hg debugrevlog -c | grep inline
+  [1]