test: expand bats coverage across installer modules

Added unit tests for `disk.sh`, `btrfs.sh`, the archangel monolith's `gather_input` unattended branch, and filled gap cases in `config.sh`. The suite grew from 71 to 110 tests.

`installer/lib/disk.sh` was completely uncovered. New `tests/unit/test_disk.bats` covers the four pure partition-path helpers (`get_efi_partition`, `get_root_partition`, `get_efi_partitions`, `get_root_partitions`) across SATA, virtio, and NVMe inputs, mixed arrays, and the empty-input behavior. Side-effecting functions in the same file (sgdisk, mkfs.fat, partprobe, and fzf wrappers) stay deliberately VM-tested.

`installer/lib/btrfs.sh` had no bats coverage. New `tests/unit/test_btrfs.bats` covers `get_luks_devices`, the only pure helper in the file. It pins the asymmetric naming convention where the first device gets the bare `LUKS_MAPPER_NAME` and subsequent devices append the index.

The archangel monolith was un-source-able for tests because its top-level code created a /tmp log file and redirected stdout via `exec > >(tee...)`, plus called `main "$@"` unconditionally at the bottom. I extracted the logging setup into an `init_logging` function called from `main`, and wrapped the main call in a `[[ "${BASH_SOURCE[0]}" == "${0}" ]]` guard. Sourcing the script now loads function definitions silently, with no log file and no banner. Running it directly works exactly as before. Verified both paths.

That refactor unlocks `tests/unit/test_archangel.bats`, which covers `gather_input` in unattended mode. Required-field validation for HOSTNAME, TIMEZONE, ROOT_PASSWORD, and DISKS. Optional-field defaulting (FILESYSTEM to zfs, LOCALE to en_US.UTF-8, KEYMAP to us, ENABLE_SSH to yes). Filesystem-specific encryption checks (ZFS_PASSPHRASE required when not NO_ENCRYPT, same for LUKS_PASSPHRASE on Btrfs). Filesystem validity. RAID_LEVEL defaulting for multi-disk installs. The interactive branch stays out of scope per the testing-strategy policy.

`tests/unit/test_config.bats` got five gap tests: `check_config` when CONFIG_FILE is set, `validate_config` against a non-block-device entry (e.g. /dev/null) and a missing path, and `parse_args` accepting `--color` and `--config-file` together in either order.

`testing-strategy.org` got an expanded "What bats does NOT cover" section. The doc previously named six tools (mkfs, cryptsetup, zpool create, pacstrap, arch-chroot, grub-install). The new list adds sgdisk, partprobe, blkid, mkfs.fat, mkfs.btrfs, snapper, efibootmgr, mount, umount, findmnt, mountpoint, and fzf. It also names the conditions (root needed, real /dev or /sys state) that make a function VM-only. The coverage table at the top now lists the three new test files.

No behavior change in production code. The init_logging extraction preserves the existing log path and banner format byte-for-byte.

1 files changed, 214 insertions, 0 deletions

diff --git a/tests/unit/test_archangel.bats b/tests/unit/test_archangel.bats
new file mode 100644
index 0000000..c31cebb
--- /dev/null
+++ b/tests/unit/test_archangel.bats
@@ -0,0 +1,214 @@
+#!/usr/bin/env bats
+# Unit tests for the installer/archangel monolith.
+#
+# Coverage scope: gather_input() in unattended mode — the validation
+# of required config values, defaulting of optional ones, and the
+# filesystem-specific encryption checks. The interactive branch
+# (everything reachable via `if [[ "$UNATTENDED" != true ]]`) is not
+# unit-tested per the project's testing-strategy.org policy on
+# fzf / arch-chroot / mkfs / cryptsetup wrappers.
+#
+# Sourcing archangel relies on the source-guard at the bottom of
+# the script: when sourced, function definitions load but main is
+# not called, init_logging is not run (so /tmp/archangel-*.log is
+# not created), and the banner is not printed.
+
+setup() {
+    # shellcheck disable=SC1091
+    source "${BATS_TEST_DIRNAME}/../../installer/archangel"
+    UNATTENDED=true
+}
+
+#############################
+# Required-field validation
+#############################
+
+@test "gather_input unattended errors when HOSTNAME is missing" {
+    HOSTNAME=""
+    TIMEZONE=UTC
+    ROOT_PASSWORD=secret
+    SELECTED_DISKS=(/dev/sda)
+    NO_ENCRYPT=yes
+    run gather_input
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"HOSTNAME"* ]]
+}
+
+@test "gather_input unattended errors when TIMEZONE is missing" {
+    HOSTNAME=h
+    TIMEZONE=""
+    ROOT_PASSWORD=secret
+    SELECTED_DISKS=(/dev/sda)
+    NO_ENCRYPT=yes
+    run gather_input
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"TIMEZONE"* ]]
+}
+
+@test "gather_input unattended errors when ROOT_PASSWORD is missing" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=""
+    SELECTED_DISKS=(/dev/sda)
+    NO_ENCRYPT=yes
+    run gather_input
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"ROOT_PASSWORD"* ]]
+}
+
+@test "gather_input unattended errors when SELECTED_DISKS is empty" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=secret
+    SELECTED_DISKS=()
+    NO_ENCRYPT=yes
+    run gather_input
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"DISKS"* ]]
+}
+
+#############################
+# Optional-field defaults
+#############################
+
+@test "gather_input unattended defaults FILESYSTEM to zfs when empty" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=""
+    NO_ENCRYPT=yes
+    gather_input >/dev/null
+    [ "$FILESYSTEM" = "zfs" ]
+}
+
+@test "gather_input unattended defaults LOCALE, KEYMAP, ENABLE_SSH when empty" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=zfs
+    NO_ENCRYPT=yes
+    LOCALE=""
+    KEYMAP=""
+    ENABLE_SSH=""
+    gather_input >/dev/null
+    [ "$LOCALE" = "en_US.UTF-8" ]
+    [ "$KEYMAP" = "us" ]
+    [ "$ENABLE_SSH" = "yes" ]
+}
+
+@test "gather_input unattended preserves explicit non-default values" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=btrfs
+    NO_ENCRYPT=yes
+    LOCALE="en_GB.UTF-8"
+    KEYMAP="dvorak"
+    ENABLE_SSH="no"
+    gather_input >/dev/null
+    [ "$FILESYSTEM" = "btrfs" ]
+    [ "$LOCALE" = "en_GB.UTF-8" ]
+    [ "$KEYMAP" = "dvorak" ]
+    [ "$ENABLE_SSH" = "no" ]
+}
+
+#############################
+# Filesystem-specific encryption validation
+#############################
+
+@test "gather_input unattended errors when ZFS without ZFS_PASSPHRASE and encryption on" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=zfs
+    NO_ENCRYPT=no
+    ZFS_PASSPHRASE=""
+    run gather_input
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"ZFS_PASSPHRASE"* ]]
+}
+
+@test "gather_input unattended errors when Btrfs without LUKS_PASSPHRASE and encryption on" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=btrfs
+    NO_ENCRYPT=no
+    LUKS_PASSPHRASE=""
+    run gather_input
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"LUKS_PASSPHRASE"* ]]
+}
+
+@test "gather_input unattended accepts ZFS with NO_ENCRYPT=yes and no passphrase" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=zfs
+    NO_ENCRYPT=yes
+    ZFS_PASSPHRASE=""
+    run gather_input
+    [ "$status" -eq 0 ]
+}
+
+#############################
+# Filesystem validity
+#############################
+
+@test "gather_input unattended errors when FILESYSTEM is neither zfs nor btrfs" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=ext4
+    NO_ENCRYPT=yes
+    run gather_input
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"Invalid FILESYSTEM"* ]]
+}
+
+#############################
+# RAID-level defaulting
+#############################
+
+@test "gather_input unattended defaults RAID_LEVEL to mirror for multi-disk install" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda /dev/sdb)
+    FILESYSTEM=zfs
+    NO_ENCRYPT=yes
+    RAID_LEVEL=""
+    gather_input >/dev/null
+    [ "$RAID_LEVEL" = "mirror" ]
+}
+
+@test "gather_input unattended preserves an explicit RAID_LEVEL on multi-disk install" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda /dev/sdb /dev/sdc)
+    FILESYSTEM=zfs
+    NO_ENCRYPT=yes
+    RAID_LEVEL="raidz1"
+    gather_input >/dev/null
+    [ "$RAID_LEVEL" = "raidz1" ]
+}
+
+@test "gather_input unattended leaves RAID_LEVEL empty for single-disk install" {
+    HOSTNAME=h
+    TIMEZONE=UTC
+    ROOT_PASSWORD=x
+    SELECTED_DISKS=(/dev/sda)
+    FILESYSTEM=zfs
+    NO_ENCRYPT=yes
+    RAID_LEVEL=""
+    gather_input >/dev/null
+    [ -z "$RAID_LEVEL" ]
+}