tests: Use OS-matched target image in install tests

Add get_target_image function to tap.nu that selects the appropriate
bootc target image based on the running OS. This avoids version
mismatches (e.g., XFS features created by newer mkfs.xfs not
recognized by older grub2).

The function parses /usr/lib/os-release and looks up the image from
hack/os-image-map.json, with fallbacks for missing configurations.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Xiaofeng Wang <henrywangxf@me.com>

Author: henrywang

tmt/tests/booted/tap.nu

@@ -19,6 +19,65 @@ export def is_composefs [] {
     $st.status.booted.composefs? != null
 }
 
+# Get the target image for install tests based on the running OS
+# This ensures the target image matches the host OS to avoid version mismatches
+# (e.g., XFS features created by newer mkfs.xfs not recognized by older grub2)
+export def get_target_image [] {
+    # Parse os-release to get ID and VERSION_ID
+    let os = open /usr/lib/os-release
+        | lines
+        | filter {|l| $l != "" and not ($l | str starts-with "#") }
+        | parse "{key}={value}"
+        | reduce -f {} {|it, acc|
+            $acc | upsert $it.key ($it.value | str trim -c '"')
+        }
+
+    let id = $os.ID
+    let version_id = $os.VERSION_ID
+
+    # Construct the key for os-image-map.json
+    let key = if $id == "centos" {
+        # CentOS uses "centos-9" or "centos-10" format
+        $"centos-($version_id)"
+    } else if $id == "fedora" {
+        $"fedora-($version_id)"
+    } else if $id == "rhel" {
+        # RHEL uses "rhel-9.8" or "rhel-10.2" format
+        $"rhel-($version_id)"
+    } else {
+        # Fallback to centos-9 for unknown distros
+        "centos-9"
+    }
+
+    # Load the os-image-map.json - try multiple possible locations
+    let possible_paths = [
+        "hack/os-image-map.json",
+        "../../../hack/os-image-map.json",
+        "/var/home/bootc/hack/os-image-map.json"
+    ]
+
+    mut image_map = null
+    for p in $possible_paths {
+        if ($p | path exists) {
+            $image_map = (open $p)
+            break
+        }
+    }
+
+    # If map not found, use default centos-9 image
+    if ($image_map == null) {
+        return "docker://quay.io/centos-bootc/centos-bootc:stream9"
+    }
+
+    let image = $image_map.base | get -i $key
+    if ($image | is-empty) {
+        # Fallback to centos-9 if key not found
+        $"docker://($image_map.base.centos-9)"
+    } else {
+        $"docker://($image)"
+    }
+}
+
 # Run a bootc install command in an isolated mount namespace.
 # This handles the common setup needed for install tests run outside a container.
 export def run_install [cmd: string] {

tmt/tests/booted/test-install-outside-container.nu

@@ -6,11 +6,9 @@
 use std assert
 use tap.nu
 
-# In this test we install a generic image mainly because it keeps
-# this test in theory independent of starting from a bootc host,
-# but also because it's useful to test "skew" between the bootc binary
-# doing the install and the target image.
-let target_image = "docker://quay.io/centos-bootc/centos-bootc:stream9"
+# Use an OS-matched target image to avoid version mismatches
+# (e.g., XFS features created by newer mkfs.xfs not recognized by older grub2)
+let target_image = (tap get_target_image)
 
 # setup filesystem
 mkdir /var/mnt

tmt/tests/booted/test-install-unified-flag.nu

@@ -12,9 +12,9 @@
 use std assert
 use tap.nu
 
-# Use a generic target image to test skew between the bootc binary doing
-# the install and the target image
-let target_image = "docker://quay.io/centos-bootc/centos-bootc:stream9"
+# Use an OS-matched target image to avoid version mismatches
+# (e.g., XFS features created by newer mkfs.xfs not recognized by older grub2)
+let target_image = (tap get_target_image)
 
 def main [] {
     tap begin "install with experimental unified storage flag"