obsolescence: add setup script for obsolescence markers exchange tests

About 3 years ago, in August 2014, the logic to select what markers to select on
push was ported from the evolve extension to Mercurial core. However, for some
unclear reasons, the tests for that logic were not ported alongside.
I realised it a couple of weeks ago while working on another push related issue.
I've made a clean up pass on the tests and they are now ready to integrate the
core test suite. This series of changesets do not change any logic. I just adds
test for logic that has been around for about 10 versions of Mercurial.

They are a patch for each test case. It makes it easier to review and postpone
one with documentation issues without rejecting the wholes series.

This patch introduce the common script that setup the basic environment for the
test cases. Once this script is in. We can accept the other patches in any
order.

Each test case comes it in own test file. It help parallelism and does not
introduce a significant overhead from having a single unified giant test file.
Here are timing  to support this claim.

# Multiple test files version:
# run-tests.py --local -j 1 test-exchange-*.t
53.40s user 6.82s system 85% cpu 1:10.76 total
52.79s user 6.97s system 85% cpu 1:09.97 total
52.94s user 6.82s system 85% cpu 1:09.69 total

# Single test file version:
# run-tests.py --local -j 1 test-exchange-obsmarkers.t
52.97s user 6.85s system 85% cpu 1:10.10 total
52.64s user 6.79s system 85% cpu 1:09.63 total
53.70s user 7.00s system 85% cpu 1:11.17 total

tests/testlib/exchange-obsmarker-util.sh

@@ -0,0 +1,133 b''
+#!/bin/sh
+# setup config and various utility to test obsolescence marker exchanges tests
+
+cat >> $HGRCPATH <<EOF
+[web]
+# We test http pull and push, drop authentication requirement
+push_ssl = false
+allow_push = *
+
+[ui]
+# simpler log output
+logtemplate ="{node|short} ({phase}): {desc}\n"
+
+[phases]
+# non publishing server
+publish=False
+
+[experimental]
+# reduce output changes
+bundle2-output-capture=True
+# enable evolution
+evolution=all
+
+[extensions]
+# we need to strip some changeset for some test cases
+hgext.strip=
+
+[alias]
+# fix date used to create obsolete markers.
+debugobsolete=debugobsolete -d '0 0'
+# poor man substiture to the evolve 'hg prune'. using prune makes the test clearer and 
+prune =!hg debugobsolete --record-parents \$1 "\$2" \`hg log --hidden --template '{node}\n' --rev "\$3"\`;\
+        hg up --quiet 'max((::.) - obsolete())'
+EOF
+
+mkcommit() {
+   echo "$1" > "$1"
+   hg add "$1"
+   hg ci -m "$1"
+}
+getid() {
+   hg log --hidden --template '{node}\n' --rev "$1"
+}
+
+setuprepos() {
+    echo creating test repo for test case $1
+    mkdir $1
+    cd $1
+    echo - pulldest
+    hg init pushdest
+    cd pushdest
+    mkcommit O
+    hg phase --public .
+    cd ..
+    echo - main
+    hg clone -q pushdest main
+    echo - pushdest
+    hg clone -q main pulldest
+    echo 'cd into `main` and proceed with env setup'
+}
+
+inspect_obsmarkers (){
+    # This exist as its own function to help the evolve extension reuse the tests as is.
+    # The evolve extensions version will includes more advances query (eg:
+    # related to obsmarkers discovery) to this.
+    echo 'obsstore content'
+    echo '================'
+    hg debugobsolete
+}
+
+dotest() {
+    # dotest TESTNAME [TARGETNODE] [PUSHFLAGS+]
+    #
+    # test exchange for the given test case.
+    #
+    # This function performs push and pull in all directions through all
+    # protocols and display the resulting obsolescence markers on all sides.
+
+    testcase=$1
+    shift
+    target="$1"
+    if [ $# -gt 0 ]; then
+        shift
+    fi
+    targetnode=""
+    desccall=""
+    cd $testcase
+    echo "## Running testcase $testcase"
+    if [ -n "$target" ]; then
+        desccall="desc("\'"$target"\'")"
+        targetnode="`hg -R main id -qr \"$desccall\"`"
+        echo "# testing echange of \"$target\" ($targetnode)"
+    fi
+    echo "## initial state"
+    echo "# obstore: main"
+    hg -R main     debugobsolete | sort
+    echo "# obstore: pushdest"
+    hg -R pushdest debugobsolete | sort
+    echo "# obstore: pulldest"
+    hg -R pulldest debugobsolete | sort
+
+    if [ -n "$target" ]; then
+        echo "## pushing \"$target\"" from main to pushdest
+        hg -R main push -r "$desccall" $@ pushdest
+    else
+        echo "## pushing from main to pushdest"
+        hg -R main push pushdest $@
+    fi
+    echo "## post push state"
+    echo "# obstore: main"
+    hg -R main     debugobsolete | sort
+    echo "# obstore: pushdest"
+    hg -R pushdest debugobsolete | sort
+    echo "# obstore: pulldest"
+    hg -R pulldest debugobsolete | sort
+    if [ -n "$target" ]; then
+        echo "## pulling \"$targetnode\"" from main into pulldest
+        hg -R pulldest pull -r $targetnode $@ main
+    else
+        echo "## pulling from main into pulldest"
+        hg -R pulldest pull main $@
+    fi
+    echo "## post pull state"
+    echo "# obstore: main"
+    hg -R main     debugobsolete | sort
+    echo "# obstore: pushdest"
+    hg -R pushdest debugobsolete | sort
+    echo "# obstore: pulldest"
+    hg -R pulldest debugobsolete | sort
+
+    cd ..
+
+}