diff --git a/tests/git-extra-utility.bats b/tests/git-extra-utility.bats
new file mode 100644
index 0000000..4874ad9
--- /dev/null
+++ b/tests/git-extra-utility.bats
@@ -0,0 +1,243 @@
+#!/usr/bin/env bats
+# shellcheck shell=bash
+
+source "$BATS_TEST_DIRNAME/test_util.sh"
+
+setup_file() {
+	test_util.setup_file
+}
+
+setup() {
+	test_util.cd_test
+	test_util.git_init
+
+	# Source the utility file
+	source "$BATS_TEST_DIRNAME/../helper/git-extra-utility"
+}
+
+# Tests for git_extra_mktemp
+@test "git_extra_mktemp: creates a temporary file" {
+	local temp_file
+	temp_file=$(git_extra_mktemp)
+
+	# Check that file was created
+	[[ -e "$temp_file" ]]
+
+	# Cleanup
+	rm -f "$temp_file"
+}
+
+@test "git_extra_mktemp: creates files with unique names" {
+	local temp_file1 temp_file2
+	temp_file1=$(git_extra_mktemp)
+	temp_file2=$(git_extra_mktemp)
+
+	# Check that files are different
+	[[ "$temp_file1" != "$temp_file2" ]]
+
+	# Cleanup
+	rm -f "$temp_file1" "$temp_file2"
+}
+
+@test "git_extra_mktemp: temp files are writable" {
+	local temp_file
+	temp_file=$(git_extra_mktemp)
+
+	# Write to the file
+	echo "test content" > "$temp_file"
+
+	# Verify content
+	[[ "$(cat "$temp_file")" == "test content" ]]
+
+	# Cleanup
+	rm -f "$temp_file"
+}
+
+# Tests for git_extra_default_branch
+@test "git_extra_default_branch: respects git-extras.default-branch config" {
+	git config git-extras.default-branch "custom-branch"
+
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "custom-branch" ]]
+}
+
+@test "git_extra_default_branch: detects from remote HEAD when origin exists" {
+	# Setup a remote with main branch (we're already on main from setup)
+	echo "content" > file.txt
+	git add file.txt
+	git commit -m "initial commit"
+
+	# Create a bare repo to act as remote
+	local remote_dir="$BATS_TEST_TMPDIR/remote.git"
+	git init --bare "$remote_dir"
+	git remote add origin "$remote_dir"
+	git push -u origin main
+	git remote set-head origin main
+
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "main" ]]
+}
+
+@test "git_extra_default_branch: respects init.defaultBranch config when no remote" {
+	git config init.defaultBranch "develop"
+
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "develop" ]]
+}
+
+@test "git_extra_default_branch: detects 'main' branch when it exists locally" {
+	# We're already on main from setup
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "main" ]]
+}
+
+@test "git_extra_default_branch: detects 'master' branch when it exists locally" {
+	# Create a new repo with master branch
+	cd "$BATS_TEST_TMPDIR"
+	rm -rf test_master
+	mkdir test_master
+	cd test_master
+	git init --initial-branch master
+	git config user.name 'Name'
+	git config user.email 'name@example.com'
+	# Need to create a commit so the branch actually exists
+	echo "content" > file.txt
+	git add file.txt
+	git commit -m "initial commit"
+
+	source "$BATS_TEST_DIRNAME/../helper/git-extra-utility"
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "master" ]]
+}
+
+@test "git_extra_default_branch: prefers 'main' over 'master' when both exist" {
+	# First commit to establish main branch
+	echo "content" > file.txt
+	git add file.txt
+	git commit -m "initial commit"
+
+	# Create master branch
+	git checkout -b master
+	echo "content2" > file2.txt
+	git add file2.txt
+	git commit -m "master commit"
+
+	# Switch back to main
+	git checkout main
+
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "main" ]]
+}
+
+@test "git_extra_default_branch: detects 'trunk' branch" {
+	# Create a new repo with trunk branch
+	cd "$BATS_TEST_TMPDIR"
+	rm -rf test_trunk
+	mkdir test_trunk
+	cd test_trunk
+	git init --initial-branch trunk
+	git config user.name 'Name'
+	git config user.email 'name@example.com'
+	# Need to create a commit so the branch actually exists
+	echo "content" > file.txt
+	git add file.txt
+	git commit -m "initial commit"
+
+	source "$BATS_TEST_DIRNAME/../helper/git-extra-utility"
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "trunk" ]]
+}
+
+@test "git_extra_default_branch: detects 'development' branch" {
+	# Create a new repo with development branch
+	cd "$BATS_TEST_TMPDIR"
+	rm -rf test_dev
+	mkdir test_dev
+	cd test_dev
+	git init --initial-branch development
+	git config user.name 'Name'
+	git config user.email 'name@example.com'
+	# Need to create a commit so the branch actually exists
+	echo "content" > file.txt
+	git add file.txt
+	git commit -m "initial commit"
+
+	source "$BATS_TEST_DIRNAME/../helper/git-extra-utility"
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "development" ]]
+}
+
+@test "git_extra_default_branch: falls back to 'main' when no branches exist" {
+	# Create a completely empty repo
+	cd "$BATS_TEST_TMPDIR"
+	rm -rf test_empty
+	mkdir test_empty
+	cd test_empty
+	git init
+	git config user.name 'Name'
+	git config user.email 'name@example.com'
+
+	source "$BATS_TEST_DIRNAME/../helper/git-extra-utility"
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "main" ]]
+}
+
+@test "git_extra_default_branch: git-extras.default-branch takes precedence over remote HEAD" {
+	# Setup a remote with main branch (we're already on main from setup)
+	echo "content" > file.txt
+	git add file.txt
+	git commit -m "initial commit"
+
+	local remote_dir="$BATS_TEST_TMPDIR/remote.git"
+	git init --bare "$remote_dir"
+	git remote add origin "$remote_dir"
+	git push -u origin main
+	git remote set-head origin main
+
+	# Set a different default in config
+	git config git-extras.default-branch "custom"
+
+	result=$(git_extra_default_branch)
+
+	# Should use config value, not remote HEAD
+	[[ "$result" == "custom" ]]
+}
+
+@test "git_extra_default_branch: git-extras.default-branch takes precedence over init.defaultBranch" {
+	git config init.defaultBranch "develop"
+	git config git-extras.default-branch "custom"
+
+	result=$(git_extra_default_branch)
+
+	[[ "$result" == "custom" ]]
+}
+
+@test "git_extra_default_branch: remote HEAD takes precedence over init.defaultBranch" {
+	# Setup a remote with main branch
+	echo "content" > file.txt
+	git add file.txt
+	git commit -m "initial commit"
+
+	local remote_dir="$BATS_TEST_TMPDIR/remote.git"
+	git init --bare "$remote_dir"
+	git remote add origin "$remote_dir"
+	git push -u origin main
+	git remote set-head origin main
+
+	# Set a different default in init config
+	git config init.defaultBranch "develop"
+
+	result=$(git_extra_default_branch)
+
+	# Should use remote HEAD, not init.defaultBranch
+	[[ "$result" == "main" ]]
+}