diff --git a/test/git/status_view_test.lua b/test/git/status_view_test.lua
new file mode 100644
index 0000000..913506d
--- /dev/null
+++ b/test/git/status_view_test.lua
@@ -0,0 +1,210 @@
+local h = require("helpers")
+
+require("git").init()
+
+---Run the cursor-restore autocmd that was responsible for the original
+---cursor-jump bug. Replicating it lets the regression test exercise the
+---same interaction the user had in their config.
+local function install_cursor_restore_autocmd()
+    vim.api.nvim_create_autocmd("BufReadPost", {
+        pattern = "*",
+        command = 'silent! normal! g`"zv',
+    })
+end
+
+---@param sidebar_buf integer
+---@param needle string
+---@return integer?
+local function find_line(sidebar_buf, needle)
+    for i, l in
+        ipairs(vim.api.nvim_buf_get_lines(sidebar_buf, 0, -1, false))
+    do
+        if l:match(needle) then
+            return i
+        end
+    end
+end
+
+---@return integer? sidebar_buf, integer? sidebar_win
+local function find_sidebar()
+    local buf, win
+    for _, b in ipairs(vim.api.nvim_list_bufs()) do
+        if vim.bo[b].filetype == "gitstatus" then
+            buf = b
+        end
+    end
+    for _, w in ipairs(vim.api.nvim_list_wins()) do
+        if vim.api.nvim_win_get_buf(w) == buf then
+            win = w
+        end
+    end
+    return buf, win
+end
+
+---@param role string
+---@return integer?
+local function find_diff_win(role)
+    for _, w in ipairs(vim.api.nvim_list_wins()) do
+        if vim.w[w].git_diff_role == role then
+            return w
+        end
+    end
+end
+
+---Set up a repo with one tracked-and-modified file, open the sidebar, and
+---return the sidebar window plus the line of the file's entry.
+---@param file_path string
+---@param committed_content string
+---@param worktree_content string
+---@return integer sidebar_win
+---@return integer entry_line
+local function setup_sidebar_with_unstaged_file(
+    file_path,
+    committed_content,
+    worktree_content
+)
+    local repo = h.make_repo({ [file_path] = committed_content })
+    h.write(repo, file_path, worktree_content)
+    vim.cmd("cd " .. repo)
+
+    require("git.status_view").open({ placement = "sidebar" })
+    local sidebar_buf, sidebar_win = find_sidebar()
+    assert(sidebar_buf, "sidebar buffer should exist")
+    assert(sidebar_win, "sidebar window should exist")
+
+    local r = assert(
+        require("git.repo").find(vim.fn.getcwd()),
+        "repo should resolve for the test worktree"
+    )
+    r:refresh()
+    vim.wait(1000, function()
+        return r.status and #r.status:by_kind("unstaged") > 0
+    end)
+
+    local entry_line = assert(
+        find_line(sidebar_buf, vim.pesc(file_path) .. "$"),
+        file_path .. " should appear in sidebar"
+    )
+    return sidebar_win, entry_line
+end
+
+local function press(keys)
+    local rhs = vim.api.nvim_replace_termcodes(keys, true, false, true)
+    vim.api.nvim_feedkeys(rhs, "x", false)
+end
+
+---@param cond fun(): boolean
+---@param msg string
+local function wait_for(cond, msg)
+    h.truthy(vim.wait(1000, cond), "timed out waiting for: " .. msg)
+end
+
+h.test(
+    "stage with diff open: sidebar cursor stays put",
+    function()
+        install_cursor_restore_autocmd()
+        local sidebar_win, line = setup_sidebar_with_unstaged_file(
+            "zsh/rc",
+            "ZSH=true\n",
+            "ZSH=true\nmodified\n"
+        )
+
+        vim.api.nvim_set_current_win(sidebar_win)
+        vim.api.nvim_win_set_cursor(sidebar_win, { line, 0 })
+
+        press("<Tab>")
+        wait_for(function()
+            return find_diff_win("left") ~= nil
+        end, "diff windows to appear")
+
+        local r = assert(require("git.repo").find(vim.fn.getcwd()))
+        vim.api.nvim_set_current_win(sidebar_win)
+        press("s")
+        wait_for(function()
+            return #r.status:by_kind("staged") > 0
+        end, "stage to propagate to repo state")
+
+        h.eq(
+            vim.api.nvim_win_get_cursor(sidebar_win),
+            { line, 0 },
+            "sidebar cursor should remain at the entry's original line"
+        )
+    end
+)
+
+h.test(
+    "stage with diff open: diff foldmethod is preserved on refresh",
+    function()
+        local sidebar_win, line = setup_sidebar_with_unstaged_file(
+            "zsh/rc",
+            "# vim: set ft=zsh nowrap:\nZSH=true\n",
+            "# vim: set ft=zsh nowrap:\nZSH=true\nmodified\n"
+        )
+
+        vim.api.nvim_set_current_win(sidebar_win)
+        vim.api.nvim_win_set_cursor(sidebar_win, { line, 0 })
+
+        press("<Tab>")
+        wait_for(function()
+            return find_diff_win("left") ~= nil
+        end, "diff windows to appear")
+        local left_win = assert(find_diff_win("left"))
+        h.eq(
+            vim.wo[left_win].foldmethod,
+            "diff",
+            "left diff foldmethod should be 'diff' after Tab"
+        )
+
+        local r = assert(require("git.repo").find(vim.fn.getcwd()))
+        vim.api.nvim_set_current_win(sidebar_win)
+        press("s")
+        wait_for(function()
+            return #r.status:by_kind("staged") > 0
+        end, "stage to propagate to repo state")
+
+        h.eq(
+            vim.wo[left_win].foldmethod,
+            "diff",
+            "left diff foldmethod should still be 'diff' after stage refresh"
+        )
+    end
+)
+
+h.test("refresh on stage updates the index URI buffer's content", function()
+    local sidebar_win, line = setup_sidebar_with_unstaged_file(
+        "foo.txt",
+        "v1\n",
+        "v2\n"
+    )
+
+    vim.api.nvim_set_current_win(sidebar_win)
+    vim.api.nvim_win_set_cursor(sidebar_win, { line, 0 })
+    press("<Tab>")
+    wait_for(function()
+        return find_diff_win("left") ~= nil
+    end, "diff windows to appear")
+
+    local left_win = assert(find_diff_win("left"))
+    local index_buf = vim.api.nvim_win_get_buf(left_win)
+    h.eq(
+        vim.api.nvim_buf_get_lines(index_buf, 0, -1, false),
+        { "v1" },
+        "index pane should initially show committed content"
+    )
+
+    vim.api.nvim_set_current_win(sidebar_win)
+    press("s")
+    wait_for(function()
+        local first =
+            vim.api.nvim_buf_get_lines(index_buf, 0, -1, false)[1]
+        return first == "v2"
+    end, "index pane to refresh to staged content")
+
+    h.eq(
+        vim.api.nvim_buf_get_lines(index_buf, 0, -1, false),
+        { "v2" },
+        "index pane should reflect staged content after refresh"
+    )
+end)
+
+h.report()
diff --git a/test/git/util_test.lua b/test/git/util_test.lua
new file mode 100644
index 0000000..a16b9c6
--- /dev/null
+++ b/test/git/util_test.lua
@@ -0,0 +1,47 @@
+local h = require("helpers")
+local util = require("git.util")
+
+h.test("set_buf_lines preserves modifiable=false", function()
+    local buf = vim.api.nvim_create_buf(false, true)
+    vim.bo[buf].modifiable = false
+    util.set_buf_lines(buf, 0, -1, { "a", "b", "c" })
+    h.eq(
+        vim.api.nvim_buf_get_lines(buf, 0, -1, false),
+        { "a", "b", "c" },
+        "lines should be replaced"
+    )
+    h.falsy(vim.bo[buf].modifiable, "modifiable should stay false")
+    h.falsy(vim.bo[buf].modified, "modified should be cleared")
+    vim.api.nvim_buf_delete(buf, { force = true })
+end)
+
+h.test("set_buf_lines preserves modifiable=true", function()
+    local buf = vim.api.nvim_create_buf(false, true)
+    vim.bo[buf].modifiable = true
+    util.set_buf_lines(buf, 0, -1, { "a", "b" })
+    h.truthy(vim.bo[buf].modifiable, "modifiable should stay true")
+    h.falsy(vim.bo[buf].modified, "modified should be cleared")
+    vim.api.nvim_buf_delete(buf, { force = true })
+end)
+
+h.test("set_buf_lines partial range update", function()
+    local buf = vim.api.nvim_create_buf(false, true)
+    vim.api.nvim_buf_set_lines(buf, 0, -1, false, { "a", "b", "c", "d" })
+    util.set_buf_lines(buf, 1, 3, { "X", "Y", "Z" })
+    h.eq(
+        vim.api.nvim_buf_get_lines(buf, 0, -1, false),
+        { "a", "X", "Y", "Z", "d" },
+        "lines [1, 3) should be replaced"
+    )
+    vim.api.nvim_buf_delete(buf, { force = true })
+end)
+
+h.test("set_buf_lines errors on out-of-bounds (strict_indexing)", function()
+    local buf = vim.api.nvim_create_buf(false, true)
+    vim.api.nvim_buf_set_lines(buf, 0, -1, false, { "a", "b" })
+    local ok = pcall(util.set_buf_lines, buf, 100, 200, { "x" })
+    h.falsy(ok, "out-of-bounds index should error")
+    vim.api.nvim_buf_delete(buf, { force = true })
+end)
+
+h.report()
diff --git a/test/helpers.lua b/test/helpers.lua
new file mode 100644
index 0000000..fa15c01
--- /dev/null
+++ b/test/helpers.lua
@@ -0,0 +1,191 @@
+local M = {}
+
+local stats = { passed = 0, failed = 0, errors = {} }
+local pending_cleanup = {}
+local started = false
+
+local color_on = vim.env.TEST_COLOR == "1"
+
+local function color(code, str)
+    if color_on then
+        return string.format("\27[%sm%s\27[0m", code, str)
+    end
+    return str
+end
+
+local function red(s)
+    return color("31", s)
+end
+
+local function green(s)
+    return color("32", s)
+end
+
+local function ensure_started()
+    if started then
+        return
+    end
+    started = true
+    io.stdout:write(
+        string.format("-> %s ", vim.env.TEST_FILE_LABEL or "?")
+    )
+    io.stdout:flush()
+end
+
+---Tear down repos created during the current test. Stops fs watchers first,
+---drains any scheduled callbacks, wipes buffers tied to the repo, then nukes
+---the directory.
+---@param dir string
+function M.cleanup(dir)
+    pcall(vim.cmd.cd, "/tmp")
+    pcall(function()
+        require("git.repo").stop_all()
+    end)
+    vim.wait(60)
+    for _, b in ipairs(vim.api.nvim_list_bufs()) do
+        local name = vim.api.nvim_buf_get_name(b)
+        if name:find(dir, 1, true) or name:match("^git[a-z]*://") then
+            pcall(vim.api.nvim_buf_delete, b, { force = true })
+        end
+    end
+    vim.fn.delete(dir, "rf")
+end
+
+---@param name string
+---@param fn fun()
+function M.test(name, fn)
+    ensure_started()
+    local ok, err = pcall(fn)
+    while #pending_cleanup > 0 do
+        local dir = table.remove(pending_cleanup)
+        pcall(M.cleanup, dir)
+    end
+    if ok then
+        stats.passed = stats.passed + 1
+        io.stdout:write(".")
+    else
+        stats.failed = stats.failed + 1
+        table.insert(stats.errors, { name = name, err = err })
+        io.stdout:write(red("F"))
+    end
+    io.stdout:flush()
+end
+
+function M.report()
+    ensure_started()
+    if stats.failed > 0 then
+        io.stdout:write(" " .. red("FAIL") .. "\n")
+        for _, e in ipairs(stats.errors) do
+            io.stdout:write(
+                string.format(
+                    "    %s %s\n      %s\n",
+                    red("FAIL"),
+                    e.name,
+                    e.err
+                )
+            )
+        end
+    else
+        io.stdout:write(" " .. green("OK") .. "\n")
+    end
+    io.stdout:write(
+        string.format("RESULTS %d %d\n", stats.passed, stats.failed)
+    )
+    if stats.failed > 0 then
+        vim.cmd("cquit 1")
+    end
+end
+
+local function fmt_value(v)
+    if type(v) == "string" then
+        return string.format("%q", v)
+    end
+    return vim.inspect(v)
+end
+
+---@param actual any
+---@param expected any
+---@param msg string?
+function M.eq(actual, expected, msg)
+    if not vim.deep_equal(actual, expected) then
+        error(
+            string.format(
+                "%s\n  expected: %s\n  actual:   %s",
+                msg or "values differ",
+                fmt_value(expected),
+                fmt_value(actual)
+            ),
+            2
+        )
+    end
+end
+
+---@param val any
+---@param msg string?
+function M.truthy(val, msg)
+    if not val then
+        error(msg or ("expected truthy, got " .. tostring(val)), 2)
+    end
+end
+
+---@param val any
+---@param msg string?
+function M.falsy(val, msg)
+    if val then
+        error(msg or ("expected falsy, got " .. tostring(val)), 2)
+    end
+end
+
+---@param dir string
+---@param ... string
+local function git(dir, ...)
+    local r = vim.system({ "git", ... }, { cwd = dir, text = true }):wait()
+    if r.code ~= 0 then
+        error(
+            string.format(
+                "git %s failed: %s",
+                table.concat({ ... }, " "),
+                vim.trim(r.stderr or "")
+            ),
+            2
+        )
+    end
+    return r
+end
+
+---@param dir string
+---@param path string
+---@param content string
+function M.write(dir, path, content)
+    local full = vim.fs.joinpath(dir, path)
+    vim.fn.mkdir(vim.fs.dirname(full), "p")
+    local f = assert(io.open(full, "w"))
+    f:write(content)
+    f:close()
+end
+
+---Create a temporary git repo and seed it with files committed on `main`.
+---The directory is auto-cleaned at the end of the current `M.test(...)`.
+---@param files table<string, string>?  path -> content
+---@return string dir
+---@return fun(...): vim.SystemCompleted runner
+function M.make_repo(files)
+    local dir = vim.fn.tempname()
+    vim.fn.mkdir(dir, "p")
+    git(dir, "init", "-q", "-b", "main")
+    git(dir, "config", "user.email", "t@t.com")
+    git(dir, "config", "user.name", "t")
+    if files and next(files) then
+        for path, content in pairs(files) do
+            M.write(dir, path, content)
+        end
+        git(dir, "add", ".")
+        git(dir, "commit", "-q", "-m", "init")
+    end
+    table.insert(pending_cleanup, dir)
+    return dir, function(...)
+        return git(dir, ...)
+    end
+end
+
+return M
diff --git a/test/run.sh b/test/run.sh
new file mode 100755
index 0000000..849c270
--- /dev/null
+++ b/test/run.sh
@@ -0,0 +1,89 @@
+#!/usr/bin/env bash
+set -u
+
+usage() {
+    cat <<EOF
+Usage: ${0##*/} [--help] [TARGET ...]
+
+Run Neovim integration tests. Each test file is invoked via
+'nvim --headless --clean' with the project's runtimepath added.
+
+With no targets, runs every test/**/*_test.lua. Each TARGET may be a
+test file (test/git/util_test.lua) or a directory (test/git); a
+directory expands to all _test.lua files beneath it.
+
+Exit status is 0 if all tests passed, non-zero otherwise.
+EOF
+}
+
+if [[ ${1:-} == --help || ${1:-} == -h ]]; then
+    usage
+    exit 0
+fi
+
+cd "$(dirname "$0")/.." || exit 1
+ROOT=$PWD
+
+if [[ -t 1 ]]; then
+    red=$'\033[31m'
+    green=$'\033[32m'
+    reset=$'\033[0m'
+    export TEST_COLOR=1
+else
+    red=''
+    green=''
+    reset=''
+fi
+
+if [[ $# -gt 0 ]]; then
+    targets=("$@")
+else
+    mapfile -d '' -t targets < <(find test -type f -name '*_test.lua' -print0 | sort -z)
+fi
+
+exit_code=0
+total_passed=0
+total_failed=0
+for arg in "${targets[@]}"; do
+    if [[ -d "$arg" ]]; then
+        mapfile -d '' -t files < <(find "$arg" -type f -name '*_test.lua' -print0 | sort -z)
+    elif [[ -f "$arg" ]]; then
+        files=("$arg")
+    else
+        printf 'no such test target: %s\n' "$arg" >&2
+        exit_code=2
+        continue
+    fi
+
+    for f in "${files[@]}"; do
+        out=$(TEST_FILE_LABEL="$f" nvim --headless --clean \
+            -c "set rtp+=$ROOT" \
+            -c "lua package.path = package.path .. ';$ROOT/test/?.lua'" \
+            -c "luafile $f" \
+            -c "qa!" \
+            2>&1)
+        rc=$?
+        # Split the per-file results from any output.
+        results_line=$(printf '%s\n' "$out" | grep '^RESULTS ' | tail -1)
+        printf '%s\n' "$out" | grep -v '^RESULTS '
+        if [[ -n "$results_line" ]]; then
+            read -r _ p f_count <<<"$results_line"
+            total_passed=$((total_passed + p))
+            total_failed=$((total_failed + f_count))
+        fi
+        if [[ $rc -ne 0 ]]; then
+            exit_code=$rc
+        fi
+    done
+done
+
+printf '\n'
+if [[ $total_failed -gt 0 ]]; then
+    printf '%s%d passed%s, %s%d failed%s\n' \
+        "$green" "$total_passed" "$reset" \
+        "$red" "$total_failed" "$reset"
+else
+    printf '%s%d passed%s\n' "$green" "$total_passed" "$reset"
+fi
+
+exit "$exit_code"