test: add (back) upgrade tests

In ee897cab8b the upgrade tests from pre v3 databases were
removed. The reasons for that are still valid, but we should still
test the code paths that do the upgrade, and it is relatively
straightforward to do that for v3 to v3 upgrades.

test/README

@@ -25,6 +25,7 @@ that you know if you break anything.
   - gdb(1)
   - gpg(1)
   - python(1)
+  - xapian-metadata(1)
 
 If your system lacks these tools or have older, non-upgradable versions
 of these, please (possibly compile and) install these to some other

test/T530-upgrade.sh

@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+test_description='database upgrades'
+. $(dirname "$0")/test-lib.sh || exit 1
+
+test_require_external_prereq xapian-metadata
+
+XAPIAN_PATH=$MAIL_DIR/.notmuch/xapian
+BACKUP_PATH=$MAIL_DIR/.notmuch
+
+delete_feature () {
+    local key=$1
+    features=$(xapian-metadata get $XAPIAN_PATH features | grep -v "^$key")
+    xapian-metadata set $XAPIAN_PATH features "$features"
+}
+
+add_email_corpus
+
+for key in 'multiple paths per message' \
+	       'relative directory paths' \
+	       'exact folder:/path: search' \
+	       'mail documents for missing messages' \
+	       'modification tracking'; do
+    backup_database
+    test_begin_subtest "upgrade is triggered by missing '$key'"
+    delete_feature "$key"
+    output=$(notmuch new | grep Welcome)
+    test_expect_equal \
+	"$output" \
+	"Welcome to a new version of notmuch! Your database will now be upgraded."
+
+    restore_database
+
+    backup_database
+    test_begin_subtest "backup can be restored ['$key']"
+    notmuch dump > BEFORE
+    delete_feature "$key"
+    notmuch new
+    notmuch tag -inbox '*'
+    dump_file=$(echo ${BACKUP_PATH}/dump*)
+    notmuch restore --input=$dump_file
+    notmuch dump > AFTER
+    test_expect_equal_file BEFORE AFTER
+    restore_database
+done
+
+for key in 'from/subject/message-ID in database' \
+	       'indexed MIME types' \
+	       'index body and headers separately'; do
+    backup_database
+    test_begin_subtest "upgrade not triggered by missing '$key'"
+    delete_feature "$key"
+    output=$(notmuch new | grep Welcome)
+    test_expect_equal "$output" ""
+    restore_database
+done
+
+test_done

test/test-lib.sh

@@ -1270,3 +1270,4 @@ test_declare_external_prereq gpg
 test_declare_external_prereq openssl
 test_declare_external_prereq gpgsm
 test_declare_external_prereq ${NOTMUCH_PYTHON}
+test_declare_external_prereq xapian-metadata