ci: create minimal unit test script

Signed-off-by: ANISH-SR <rawatanish08@gmail.com>

Author: ANISH-SR

.buildkite/main-tests.json

@@ -27,7 +27,7 @@
     },
     {
       "test_name": "unittests-gnu",
-      "command": "cargo test --all-features --workspace",
+      "command": ".buildkite/selective-tests.sh unittests-gnu",
       "platform": [
         "x86_64",
         "aarch64",
@@ -39,7 +39,7 @@
     },
     {
       "test_name": "unittests-musl",
-      "command": "cargo test --all-features --workspace --target {target_platform}-unknown-linux-musl --exclude vhost-device-gpu",
+      "command": ".buildkite/selective-tests.sh unittests-musl {target_platform}",
       "platform": [
         "x86_64",
         "aarch64"
@@ -50,7 +50,7 @@
     },
     {
       "test_name": "unittests-gnu-release",
-      "command": "cargo test --release --all-features --workspace",
+      "command": ".buildkite/selective-tests.sh unittests-gnu-release",
       "platform": [
         "x86_64",
         "aarch64",
@@ -62,7 +62,7 @@
     },
     {
       "test_name": "unittests-musl-release",
-      "command": "cargo test --release --all-features --workspace --target {target_platform}-unknown-linux-musl --exclude vhost-device-gpu",
+      "command": ".buildkite/selective-tests.sh unittests-musl-release {target_platform}",
       "platform": [
         "x86_64",
         "aarch64"

.buildkite/selective-tests.sh

@@ -0,0 +1,128 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+mode="${1:-}"; shift || true
+
+if [[ -z "${mode}" ]]; then
+    echo "Usage: selective-tests.sh <mode> [args...]" >&2
+    exit 1
+fi
+
+# Determine changed files compared to main
+if git fetch origin main >/dev/null 2>&1; then
+    changed_files=$(git diff --name-only origin/main...HEAD || true)
+else
+    changed_files=$(git diff --name-only HEAD~1..HEAD || true)
+fi
+
+if [[ -z "${changed_files}" ]]; then
+    # No diff detected, run full workspace tests to be safe
+    changed_files="__none__"
+fi
+
+workspace_changed=0
+
+# Files that we consider "workspace-wide" changes
+for f in ${changed_files}; do
+    case "${f}" in
+        Cargo.toml|Cargo.lock|rustfmt.toml|.buildkite/*|xtask/*)
+            workspace_changed=1
+            ;;
+    esac
+done
+
+# Map paths to crates
+crates=(
+    vhost-device-can
+    vhost-device-console
+    vhost-device-gpio
+    vhost-device-gpu
+    vhost-device-i2c
+    vhost-device-input
+    vhost-device-rng
+    vhost-device-scsi
+    vhost-device-scmi
+    vhost-device-sound
+    vhost-device-spi
+    vhost-device-template
+    vhost-device-vsock
+)
+
+affected_crates=()
+for f in ${changed_files}; do
+    for c in "${crates[@]}"; do
+        case "${f}" in
+            "${c}"/*)
+                affected_crates+=("${c}")
+                ;;
+        esac
+    done
+done
+
+# Unique affected crates
+if ((${#affected_crates[@]} > 0)); then
+    mapfile -t affected_crates < <(printf '%s
+' "${affected_crates[@]}" | sort -u)
+fi
+
+run_full_workspace=0
+if [[ "${workspace_changed}" -eq 1 || ${#affected_crates[@]} -eq 0 ]]; then
+    run_full_workspace=1
+fi
+
+cmd=(cargo test)
+
+case "${mode}" in
+    unittests-gnu)
+        cmd+=(--all-features)
+        ;;
+    unittests-gnu-release)
+        cmd+=(--release --all-features)
+        ;;
+    unittests-musl)
+        target_platform="${1:-}"; shift || true
+        if [[ -z "${target_platform:-}" ]]; then
+            echo "target_platform argument required for unittests-musl" >&2
+            exit 1
+        fi
+        cmd+=(--all-features --target "${target_platform}-unknown-linux-musl")
+        ;;
+    unittests-musl-release)
+        target_platform="${1:-}"; shift || true
+        if [[ -z "${target_platform:-}" ]]; then
+            echo "target_platform argument required for unittests-musl-release" >&2
+            exit 1
+        fi
+        cmd+=(--release --all-features --target "${target_platform}-unknown-linux-musl")
+        ;;
+    *)
+        echo "Unknown mode: ${mode}" >&2
+        exit 1
+        ;;
+esac
+
+if [[ "${run_full_workspace}" -eq 1 ]]; then
+    # Preserve previous behaviour: run on entire workspace.
+    if [[ "${mode}" == "unittests-musl" || "${mode}" == "unittests-musl-release" ]]; then
+        # Original musl commands excluded vhost-device-gpu.
+        cmd+=(--workspace --exclude vhost-device-gpu)
+    else
+        cmd+=(--workspace)
+    fi
+else
+    # Run only for affected crates. For musl jobs, skip vhost-device-gpu as before.
+    for c in "${affected_crates[@]}"; do
+        if [[ "${mode}" == unittests-musl* && "${c}" == "vhost-device-gpu" ]]; then
+            continue
+        fi
+        cmd+=(-p "${c}")
+    done
+
+    if ((${#affected_crates[@]} == 0)); then
+        # Nothing to run
+        echo "No affected crates to test; exiting." >&2
+        exit 0
+    fi
+fi
+
+exec "${cmd[@]}"