test: add BATS test suite (79 tests)

- tests/common.bats: PROJECT_ROOT detection, is_cmd, timestamp, data_dir,
  logging functions, color handling, require_root
- tests/detect.bats: GPU sysfs reads with mock sysfs tree, kernel param
  parsing (word boundary, dot escaping, edge positions), recommended
  GTT/pages computation (64GB, 128GB, tiny, zero), firmware bad detection,
  stack detection
- tests/format.bats: human_bytes (0, KiB, MiB, GiB boundaries, 64GiB),
  human_mib (sub-GiB, exact-GiB, recommended values, empty input)
- tests/benchmark_compare.bats: improvement/regression display, empty
  results, missing files, usage output, config change detection
- tests/log_metrics.bats: CSV header, data format, field count, input
  validation, unknown argument handling
- tests/test_helper.sh: mock sysfs tree builder, bats-assert/support setup

Makefile: add 'make test' target

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/common.bats

@@ -0,0 +1,121 @@
+#!/usr/bin/env bats
+# Tests for lib/common.sh — core utilities
+
+load test_helper.sh
+
+setup() {
+    source_lib common.sh
+}
+
+# ── PROJECT_ROOT detection ───────────────────────────────
+
+@test "PROJECT_ROOT points to a directory containing Makefile" {
+    [ -f "$PROJECT_ROOT/Makefile" ]
+}
+
+@test "PROJECT_ROOT is not the filesystem root" {
+    [ "$PROJECT_ROOT" != "/" ]
+}
+
+# ── is_cmd ───────────────────────────────────────────────
+
+@test "is_cmd: bash exists" {
+    run is_cmd bash
+    assert_success
+}
+
+@test "is_cmd: nonexistent command fails" {
+    run is_cmd this_command_does_not_exist_xyz123
+    assert_failure
+}
+
+@test "is_cmd: empty argument fails" {
+    run is_cmd ""
+    assert_failure
+}
+
+# ── timestamp ────────────────────────────────────────────
+
+@test "timestamp: returns YYYYMMDD-HHMMSS format" {
+    run timestamp
+    assert_success
+    [[ "$output" =~ ^[0-9]{8}-[0-9]{6}$ ]]
+}
+
+@test "timestamp: returns a reasonable date (not epoch)" {
+    local ts
+    ts="$(timestamp)"
+    local year="${ts:0:4}"
+    (( year >= 2025 ))
+}
+
+# ── data_dir ─────────────────────────────────────────────
+
+@test "data_dir: creates directory and returns path" {
+    local dir
+    dir="$(data_dir "test-tmp-$$")"
+    [ -d "$dir" ]
+    rmdir "$dir"
+}
+
+@test "data_dir: default returns data/ under project root" {
+    local dir
+    dir="$(data_dir ".")"
+    [[ "$dir" == "$PROJECT_ROOT/data/." ]]
+}
+
+# ── logging functions produce output ─────────────────────
+
+@test "log_info: produces output" {
+    run log_info "test message"
+    assert_success
+    assert_output --partial "test message"
+}
+
+@test "log_success: produces output" {
+    run log_success "it worked"
+    assert_success
+    assert_output --partial "it worked"
+}
+
+@test "log_warn: produces output" {
+    run log_warn "warning"
+    assert_success
+    assert_output --partial "warning"
+}
+
+@test "log_error: produces output on stderr" {
+    run log_error "failure"
+    assert_success
+    # log_error writes to stderr but bats captures both
+    assert_output --partial "failure"
+}
+
+@test "log_header: produces output with delimiters" {
+    run log_header "Section Title"
+    assert_success
+    assert_output --partial "Section Title"
+}
+
+# ── Color handling ───────────────────────────────────────
+
+@test "colors are empty strings when not a terminal" {
+    export TERM=dumb
+    # Re-source to pick up non-terminal detection
+    unset RED GREEN YELLOW BLUE CYAN BOLD DIM RESET
+    source_lib common.sh
+    # When stdout is not a tty (as in bats), colors should be empty
+    [ -z "$RED" ] || [ "$RED" = "" ]
+}
+
+# ── require_root ─────────────────────────────────────────
+
+@test "require_root: exits with error when not root" {
+    # We're not running tests as root
+    if [ "$EUID" -eq 0 ]; then
+        skip "Test must not run as root"
+    fi
+    run require_root
+    assert_failure
+    assert_output --partial "root"
+}