diff --git a/test_git.sh b/test_git.sh
new file mode 100755
index 0000000..97dc4e8
--- /dev/null
+++ b/test_git.sh
@@ -0,0 +1,988 @@
+#!/bin/bash
+#
+# Copyright 2023 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+function fail() {
+    echo "FAIL:" "$@" >&3
+    return 42
+}
+
+function pass() {
+    echo "PASS"
+}
+
+function assert_file_exists() {
+    if ! [[ -f "$1" ]]; then
+        fail "$1 does not exist"
+    fi
+}
+
+function assert_file_absent() {
+    if [[ -f "$1" ]]; then
+        fail "$1 exists but should not"
+    fi
+}
+
+function assert_eq() {
+    if [[ "$1" == "$2" ]]; then
+        return
+    fi
+    fail "'$1' does not equal '$2'"
+}
+
+function assert_substr() {
+    if [[ "$1" =~ "$2" ]]; then
+        return
+    fi
+    fail "'$1' does not contain '$2'"
+}
+
+# DIR is the directory in which all this test's state lives.
+RUNID="${RANDOM}${RANDOM}"
+DIR="/tmp/git-sync-git.$RUNID"
+mkdir "$DIR"
+
+# WORKDIR is where test cases run
+WORKDIR="$DIR/work"
+function clean_workdir() {
+    rm -rf "$WORKDIR"
+    mkdir -p "$WORKDIR"
+}
+
+#
+# After all the test functions are defined, we can iterate over them and run
+# them all automatically.  See the end of this file.
+#
+
+##############################################
+# Test `git init` on an existing repo
+##############################################
+function git::reinit_existing_repo() {
+    git init -b main
+    date > file
+    git add file 
+    git commit -qam 'commit_1'
+    TREE1="$(git ls-tree HEAD | cut -d' ' -f3 | cut -f1)"
+    git init
+    TREE2="$(git ls-tree HEAD | cut -d' ' -f3 | cut -f1)"
+    assert_eq "$TREE1" "$TREE2"
+}
+
+##############################################
+# Test `git fetch` of a branch
+##############################################
+function git::fetch_upstream_branch() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b main
+
+    # A commit on branch 1
+    git checkout -b upstream_branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+
+    # A commit on branch 2
+    git checkout -b upstream_branch_2
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+
+    popd >/dev/null
+
+    mkdir clone
+    cd clone
+    git init -b clone_branch
+
+    assert_substr "$(git cat-file -t "$SHA1" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+
+    git fetch "file://$WORKDIR/upstream" upstream_branch_1
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA1"
+    assert_file_exists file_1
+    assert_file_absent file_2
+
+    git fetch "file://$WORKDIR/upstream" upstream_branch_2
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    git checkout "$SHA2"
+    assert_file_exists file_1
+    assert_file_exists file_2
+}
+
+##############################################
+# Test `git fetch` of a tag
+##############################################
+function git::fetch_upstream_tag() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b main
+
+    # A tag on branch 1 (not at HEAD)
+    git checkout -b upstream_branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+    git tag upstream_tag_1
+
+    # Another tag on branch 1 (at HEAD)
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+    git tag upstream_tag_2
+
+    # A tag on branch 2 (not at HEAD)
+    git checkout -b upstream_branch_2
+    date > file_3
+    git add file_3
+    git commit -qam 'commit_3'
+    SHA3="$(git rev-parse HEAD)"
+    git tag upstream_tag_3
+
+    # Another tag on branch 2 (at HEAD)
+    date > file_4
+    git add file_4
+    git commit -qam 'commit_4'
+    SHA4="$(git rev-parse HEAD)"
+    git tag upstream_tag_4
+
+    popd >/dev/null
+
+    mkdir clone
+    pushd clone >/dev/null
+    git init -b clone_branch
+
+    assert_substr "$(git cat-file -t "$SHA1" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+
+    git fetch "file://$WORKDIR/upstream" upstream_tag_1
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA1"
+    assert_file_exists file_1
+    assert_file_absent file_2
+    assert_file_absent file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" upstream_tag_2
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA2"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_absent file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" upstream_tag_3
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_eq "$(git cat-file -t "$SHA3")" "commit"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA3"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_exists file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" upstream_tag_4
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_eq "$(git cat-file -t "$SHA3")" "commit"
+    assert_eq "$(git cat-file -t "$SHA4")" "commit"
+    git checkout "$SHA4"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_exists file_3
+    assert_file_exists file_4
+}
+
+##############################################
+# Test `git fetch` of an annotated tag
+##############################################
+function git::fetch_upstream_tag_annotated() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b main
+
+    # A tag on branch 1 (not at HEAD)
+    git checkout -b upstream_branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+    git tag -am "anntag_1" upstream_anntag_1
+
+    # Another tag on branch 1 (at HEAD)
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+    git tag -am "anntag_2" upstream_anntag_2
+
+    # A tag on branch 2 (not at HEAD)
+    git checkout -b upstream_branch_2
+    date > file_3
+    git add file_3
+    git commit -qam 'commit_3'
+    SHA3="$(git rev-parse HEAD)"
+    git tag -am "anntag_3" upstream_anntag_3
+
+    # Another tag on branch 2 (at HEAD)
+    date > file_4
+    git add file_4
+    git commit -qam 'commit_4'
+    SHA4="$(git rev-parse HEAD)"
+    git tag -am "anntag_4" upstream_anntag_4
+
+    popd >/dev/null
+
+    mkdir clone
+    pushd clone >/dev/null
+    git init -b clone_branch
+
+    assert_substr "$(git cat-file -t "$SHA1" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+
+    git fetch "file://$WORKDIR/upstream" upstream_anntag_1
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA1"
+    assert_file_exists file_1
+    assert_file_absent file_2
+    assert_file_absent file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" upstream_anntag_2
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA2"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_absent file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" upstream_anntag_3
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_eq "$(git cat-file -t "$SHA3")" "commit"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA3"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_exists file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" upstream_anntag_4
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_eq "$(git cat-file -t "$SHA3")" "commit"
+    assert_eq "$(git cat-file -t "$SHA4")" "commit"
+    git checkout "$SHA4"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_exists file_3
+    assert_file_exists file_4
+}
+
+##############################################
+# Test `git fetch` of a SHA
+##############################################
+function git::fetch_upstream_sha() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b main
+
+    # A commit on branch 1 (not at HEAD)
+    git checkout -b upstream_branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+
+    # Another commit on branch 1 (at HEAD)
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+
+    # A commit on branch 2 (not at HEAD)
+    git checkout -b upstream_branch_2
+    date > file_3
+    git add file_3
+    git commit -qam 'commit_3'
+    SHA3="$(git rev-parse HEAD)"
+
+    # Another commit on branch 2 (at HEAD)
+    date > file_4
+    git add file_4
+    git commit -qam 'commit_4'
+    SHA4="$(git rev-parse HEAD)"
+
+    popd >/dev/null
+
+    mkdir clone
+    pushd clone >/dev/null
+    git init -b clone_branch
+
+    assert_substr "$(git cat-file -t "$SHA1" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+
+    git fetch "file://$WORKDIR/upstream" "$SHA1"
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_substr "$(git cat-file -t "$SHA2" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA1"
+    assert_file_exists file_1
+    assert_file_absent file_2
+    assert_file_absent file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" "$SHA2"
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_substr "$(git cat-file -t "$SHA3" 2>&1 || true)" "could not get object info"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA2"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_absent file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" "$SHA3"
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_eq "$(git cat-file -t "$SHA3")" "commit"
+    assert_substr "$(git cat-file -t "$SHA4" 2>&1 || true)" "could not get object info"
+    git checkout "$SHA3"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_exists file_3
+    assert_file_absent file_4
+
+    git fetch "file://$WORKDIR/upstream" "$SHA4"
+    assert_eq "$(git cat-file -t "$SHA1")" "commit"
+    assert_eq "$(git cat-file -t "$SHA2")" "commit"
+    assert_eq "$(git cat-file -t "$SHA3")" "commit"
+    assert_eq "$(git cat-file -t "$SHA4")" "commit"
+    git checkout "$SHA4"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_file_exists file_3
+    assert_file_exists file_4
+}
+
+##############################################
+# Test git shallow fetch from a branch
+##############################################
+function git::shallow_fetch_branch() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b upstream_branch
+
+    # Some commits
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA="$(git rev-parse HEAD)"
+
+    popd >/dev/null
+
+    mkdir clone
+    cd clone
+    git init -b clone_branch
+
+    git fetch "file://$WORKDIR/upstream" upstream_branch
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+
+    git fetch "file://$WORKDIR/upstream" upstream_branch --depth 1
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "true"
+
+    git fetch "file://$WORKDIR/upstream" upstream_branch --unshallow
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+}
+
+##############################################
+# Test git shallow fetch from a tag
+##############################################
+function git::shallow_fetch_tag() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b upstream_branch
+
+    # Some commits
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA="$(git rev-parse HEAD)"
+    git tag upstream_tag
+
+    popd >/dev/null
+
+    mkdir clone
+    cd clone
+    git init -b clone_branch
+
+    git fetch "file://$WORKDIR/upstream" upstream_tag
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+
+    git fetch "file://$WORKDIR/upstream" upstream_tag --depth 1
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "true"
+
+    git fetch "file://$WORKDIR/upstream" upstream_tag --unshallow
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+}
+
+##############################################
+# Test git shallow fetch from an annotated tag
+##############################################
+function git::shallow_fetch_tag_annotated() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b upstream_branch
+
+    # Some commits
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA="$(git rev-parse HEAD)"
+    git tag -am "upstream_anntag" upstream_anntag
+
+    popd >/dev/null
+
+    mkdir clone
+    cd clone
+    git init -b clone_branch
+
+    git fetch "file://$WORKDIR/upstream" upstream_anntag
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+
+    git fetch "file://$WORKDIR/upstream" upstream_anntag --depth 1
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "true"
+
+    git fetch "file://$WORKDIR/upstream" upstream_anntag --unshallow
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+}
+
+##############################################
+# Test git shallow fetch from a SHA
+##############################################
+function git::shallow_fetch_sha() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b upstream_branch
+
+    # Some commits
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA="$(git rev-parse HEAD)"
+
+    popd >/dev/null
+
+    mkdir clone
+    cd clone
+    git init -b clone_branch
+
+    git fetch "file://$WORKDIR/upstream" "$SHA"
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+
+    git fetch "file://$WORKDIR/upstream" "$SHA" --depth 1
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "true"
+
+    git fetch "file://$WORKDIR/upstream" "$SHA" --unshallow
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+}
+
+##############################################
+# Test git fetch with depth too large
+##############################################
+function git::fetch_too_large_depth() {
+    mkdir upstream
+    pushd upstream >/dev/null
+    git init -b upstream_branch
+
+    # Some commits
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA="$(git rev-parse HEAD)"
+
+    popd >/dev/null
+
+    mkdir clone
+    cd clone
+    git init -b clone_branch
+
+    git fetch "file://$WORKDIR/upstream" upstream_branch --depth 1000
+    git checkout "$SHA"
+    assert_file_exists file_1
+    assert_file_exists file_2
+    assert_eq "$(git rev-parse --is-shallow-repository)" "false"
+}
+
+##############################################
+# Test git rev-parse with a branch
+##############################################
+function git::rev_parse_branch() {
+    mkdir repo
+    pushd repo >/dev/null
+    git init -b main
+
+    # A commit on branch 1
+    git checkout -b branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+
+    # A commit on branch 2
+    git checkout -b branch_2
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+
+    assert_eq "$(git rev-parse branch_1)" "$SHA1"
+    assert_eq "$(git rev-parse branch_1^{commit})" "$SHA1"
+    assert_eq "$(git rev-parse branch_2)" "$SHA2"
+    assert_eq "$(git rev-parse branch_2^{commit})" "$SHA2"
+}
+
+##############################################
+# Test git rev-parse with a tag
+##############################################
+function git::rev_parse_tag() {
+    mkdir repo
+    pushd repo >/dev/null
+    git init -b main
+
+    # A tag on branch 1 (not at HEAD)
+    git checkout -b branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+    git tag tag_1
+
+    # Another tag on branch 1 (at HEAD)
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+    git tag tag_2
+
+    # A tag on branch 2 (not at HEAD)
+    git checkout -b branch_2
+    date > file_3
+    git add file_3
+    git commit -qam 'commit_3'
+    SHA3="$(git rev-parse HEAD)"
+    git tag tag_3
+
+    # Another tag on branch 2 (at HEAD)
+    date > file_4
+    git add file_4
+    git commit -qam 'commit_4'
+    SHA4="$(git rev-parse HEAD)"
+    git tag tag_4
+
+    assert_eq "$(git rev-parse tag_1)" "$SHA1"
+    assert_eq "$(git rev-parse tag_1^{commit})" "$SHA1"
+    assert_eq "$(git rev-parse tag_2)" "$SHA2"
+    assert_eq "$(git rev-parse tag_2^{commit})" "$SHA2"
+    assert_eq "$(git rev-parse tag_3)" "$SHA3"
+    assert_eq "$(git rev-parse tag_3^{commit})" "$SHA3"
+    assert_eq "$(git rev-parse tag_4)" "$SHA4"
+    assert_eq "$(git rev-parse tag_4^{commit})" "$SHA4"
+}
+
+##############################################
+# Test git rev-parse with an annotated tag
+##############################################
+function git::rev_parse_tag_annotated() {
+    mkdir repo
+    pushd repo >/dev/null
+    git init -b main
+
+    # A tag on branch 1 (not at HEAD)
+    git checkout -b branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+    git tag -am "anntag_1" anntag_1
+
+    # Another tag on branch 1 (at HEAD)
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+    git tag -am "anntag_2" anntag_2
+
+    # A tag on branch 2 (not at HEAD)
+    git checkout -b branch_2
+    date > file_3
+    git add file_3
+    git commit -qam 'commit_3'
+    SHA3="$(git rev-parse HEAD)"
+    git tag -am "anntag_3" anntag_3
+
+    # Another tag on branch 2 (at HEAD)
+    date > file_4
+    git add file_4
+    git commit -qam 'commit_4'
+    SHA4="$(git rev-parse HEAD)"
+    git tag -am "anntag_4" anntag_4
+
+    # Annotated tags have their own SHA, which can be found with rev-parse, but
+    # it doesn't make sense to test rev-parse against itself.
+    assert_eq "$(git rev-parse anntag_1^{commit})" "$SHA1"
+    assert_eq "$(git rev-parse anntag_2^{commit})" "$SHA2"
+    assert_eq "$(git rev-parse anntag_3^{commit})" "$SHA3"
+    assert_eq "$(git rev-parse anntag_4^{commit})" "$SHA4"
+}
+
+##############################################
+# Test git rev-parse with a SHA
+##############################################
+function git::rev_parse_sha() {
+    mkdir repo
+    pushd repo >/dev/null
+    git init -b main
+
+    # A commit on branch 1 (not at HEAD)
+    git checkout -b branch_1
+    date > file_1
+    git add file_1
+    git commit -qam 'commit_1'
+    SHA1="$(git rev-parse HEAD)"
+    SHORT1="$(echo "$SHA1" | sed 's/........$//')"
+
+    # Another commit on branch 1 (at HEAD)
+    date > file_2
+    git add file_2
+    git commit -qam 'commit_2'
+    SHA2="$(git rev-parse HEAD)"
+    SHORT2="$(echo "$SHA2" | sed 's/........$//')"
+
+    # A commit on branch 2 (not at HEAD)
+    git checkout -b branch_2
+    date > file_3
+    git add file_3
+    git commit -qam 'commit_3'
+    SHA3="$(git rev-parse HEAD)"
+    SHORT3="$(echo "$SHA3" | sed 's/........$//')"
+
+    # Another commit on branch 2 (at HEAD)
+    date > file_4
+    git add file_4
+    git commit -qam 'commit_4'
+    SHA4="$(git rev-parse HEAD)"
+    SHORT4="$(echo "$SHA4" | sed 's/........$//')"
+
+    assert_eq "$(git rev-parse "$SHA1")" "$SHA1"
+    assert_eq "$(git rev-parse "$SHA1^{commit}")" "$SHA1"
+    assert_eq "$(git rev-parse "$SHORT1")" "$SHA1"
+    assert_eq "$(git rev-parse "$SHA2")" "$SHA2"
+    assert_eq "$(git rev-parse "$SHA2^{commit}")" "$SHA2"
+    assert_eq "$(git rev-parse "$SHORT2")" "$SHA2"
+    assert_eq "$(git rev-parse "$SHA3")" "$SHA3"
+    assert_eq "$(git rev-parse "$SHA3^{commit}")" "$SHA3"
+    assert_eq "$(git rev-parse "$SHORT3")" "$SHA3"
+    assert_eq "$(git rev-parse "$SHA4")" "$SHA4"
+    assert_eq "$(git rev-parse "$SHA4^{commit}")" "$SHA4"
+    assert_eq "$(git rev-parse "$SHORT4")" "$SHA4"
+}
+
+##############################################
+# Test git rev-parse with a non-existent ref
+##############################################
+function git::rev_parse_non_existent_name() {
+    mkdir repo
+    pushd repo >/dev/null
+    git init -b main
+
+    assert_substr "$(git rev-parse does-not-exist 2>&1 || true)" "unknown revision"
+}
+
+##############################################
+# Test git rev-parse with a non-existent sha
+##############################################
+function git::rev_parse_non_existent_sha() {
+    mkdir repo
+    pushd repo >/dev/null
+    git init -b main
+
+    # As long as it tastes like a SHA, rev-parse is happy, but there is no
+    # commit for it.
+    assert_eq "$(git rev-parse 0123456789abcdef0123456789abcdef01234567)" "0123456789abcdef0123456789abcdef01234567"
+    assert_substr "$(git rev-parse 0123456789abcdef0123456789abcdef01234567^{commit} 2>&1 || true)" "unknown revision"
+    # Less-than-full SHAs do not work.
+    assert_substr "$(git rev-parse 0123456789abcdef 2>&1 || true)" "unknown revision"
+    assert_substr "$(git rev-parse 0123456789abcdef^{commit} 2>&1 || true)" "unknown revision"
+}
+
+#
+# main
+#
+
+function list_tests() {
+    (
+        shopt -s extdebug
+        declare -F \
+            | cut -f3 -d' ' \
+            | grep "^git::" \
+            | while read X; do declare -F $X; done \
+            | sort -n -k2 \
+            | cut -f1 -d' ' \
+            | sed 's/^git:://'
+    )
+}
+
+# Figure out which, if any, tests to run.
+all_tests=($(list_tests))
+tests_to_run=()
+
+function print_tests() {
+    echo "available tests:"
+    for t in "${all_tests[@]}"; do
+        echo "    $t"
+    done
+}
+
+# Validate and accumulate tests to run if args are specified.
+for arg; do
+    # Use -? to list known tests.
+    if [[ "${arg}" == "-?" ]]; then
+        print_tests
+        exit 0
+    fi
+    if [[ "${arg}" =~ ^- ]]; then
+        echo "ERROR: unknown flag '${arg}'"
+        exit 1
+    fi
+    # Make sure each non-flag arg matches at least one test.
+    nmatches=0
+    for t in "${all_tests[@]}"; do
+        if [[ "${t}" =~ ${arg} ]]; then
+            nmatches=$((nmatches+1))
+            # Don't run tests twice, just keep the first match.
+            if [[ " ${tests_to_run[*]} " =~ " ${t} " ]]; then
+                continue
+            fi
+            tests_to_run+=("${t}")
+            continue
+        fi
+    done
+    if [[ ${nmatches} == 0 ]]; then
+        echo "ERROR: no tests match pattern '${arg}'"
+        echo
+        print_tests
+        exit 1
+    fi
+    tests_to_run+=("${matches[@]}")
+done
+set -- "${tests_to_run[@]}"
+
+# If no tests were specified, run them all.
+if [[ "$#" == 0 ]]; then
+    set -- "${all_tests[@]}"
+fi
+
+function finish() {
+  r=$?
+  trap "" INT EXIT ERR
+  if [[ $r != 0 ]]; then
+    echo
+    echo "the directory $DIR was not removed as it contains"\
+         "log files useful for debugging"
+  fi
+  exit $r
+}
+trap finish INT EXIT ERR
+
+echo
+echo "test root is $DIR"
+echo
+
+# Run a test function and return its error code.  This is needed because POSIX
+# dictates that `errexit` does not apply inside a function called in an `if`
+# context.  But if we don't call it with `if`, then it terminates the whole
+# test run as soon as one test fails.  So this jumps through hoops to let the
+# individual test functions run outside of `if` and return a code in a
+# variable.
+#
+# Args:
+#  $1: the name of a variable to populate with the return code
+#  $2+: the test function to run and optional args
+function run_test() {
+    retvar=$1
+    shift
+
+    declare -g "$retvar"
+    local restore_opts=$(set +o)
+    set +o errexit
+    set +o nounset
+    set +o pipefail
+    (
+        set -o errexit
+        set -o nounset
+        set -o pipefail
+        "$@"
+    )
+    eval "$retvar=$?"
+    eval "$restore_opts"
+}
+
+# Override local configs for predictability in this test.
+export GIT_CONFIG_GLOBAL=/dev/null
+export GIT_CONFIG_SYSTEM=/dev/null
+
+# TODO: add a flag to run all the tests inside the git-sync container image
+# Iterate over the chosen tests and run them.
+FAILS=()
+FINAL_RET=0
+RUNS="${RUNS:-1}"
+for t; do
+    TEST_RET=0
+    RUN=0
+    while [[ "${RUN}" < "${RUNS}" ]]; do
+        clean_workdir
+
+        pushd "$WORKDIR" >/dev/null
+
+        sfx=""
+        if [[ "${RUNS}" > 1 ]]; then
+            sfx=" ($((RUN+1))/${RUNS})"
+        fi
+        echo -n "testcase ${t}${sfx}: "
+
+        # Set &3 for our own output, let testcases use &2 and &1.
+        exec 3>&1
+
+        # See comments on run_test for details.
+        RUN_RET=0
+        LOG="${DIR}/log.$t"
+        run_test RUN_RET "git::${t}" >"${LOG}.${RUN}" 2>&1
+        if [[ "$RUN_RET" == 0 ]]; then
+            pass
+        else
+            TEST_RET=1
+            if [[ "$RUN_RET" != 42 ]]; then
+                echo "FAIL: unknown error"
+            fi
+        fi
+        RUN=$((RUN+1))
+
+        popd >/dev/null
+    done
+    if [[ "$TEST_RET" != 0 ]]; then
+        FINAL_RET=1
+        FAILS+=("$t  (log: ${LOG}.*)")
+    fi
+done
+if [[ "$FINAL_RET" != 0 ]]; then
+    echo
+    echo "the following tests failed:"
+    for f in "${FAILS[@]}"; do
+        echo "    $f"
+    done
+    exit 1
+fi
+
+# Finally...
+echo
+if [[ "${CLEANUP:-}" == 0 ]]; then
+    echo "leaving logs in $DIR"
+else
+    rm -rf "$DIR"
+fi
+