diff --git a/bin/tests/test-deploy-skill.sh b/bin/tests/test-deploy-skill.sh
new file mode 100755
index 0000000..6e00c9d
--- /dev/null
+++ b/bin/tests/test-deploy-skill.sh
@@ -0,0 +1,299 @@
+#!/usr/bin/env bash
+# Tests for deploy-skill.sh config injection functions
+# Run: bash bin/tests/test-deploy-skill.sh
+
+set -uo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PASSED=0
+FAILED=0
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+NC='\033[0m' # No Color
+
+# Extract inject_nix_config function
+eval "$(sed -n '/^inject_nix_config()/,/^}/p' "$SCRIPT_DIR/../deploy-skill.sh")"
+
+# Extract inject_home_file function
+eval "$(sed -n '/^inject_home_file()/,/^}/p' "$SCRIPT_DIR/../deploy-skill.sh")"
+
+# Test helpers
+assert_contains() {
+    local description="$1"
+    local pattern="$2"
+    local file="$3"
+
+    if grep -q "$pattern" "$file" 2>/dev/null; then
+        echo -e "${GREEN}PASS${NC}: $description"
+        ((PASSED++))
+    else
+        echo -e "${RED}FAIL${NC}: $description"
+        echo "  Pattern not found: '$pattern'"
+        echo "  File contents:"
+        cat "$file" | sed 's/^/    /'
+        ((FAILED++))
+    fi
+}
+
+assert_not_contains() {
+    local description="$1"
+    local pattern="$2"
+    local file="$3"
+
+    if ! grep -q "$pattern" "$file" 2>/dev/null; then
+        echo -e "${GREEN}PASS${NC}: $description"
+        ((PASSED++))
+    else
+        echo -e "${RED}FAIL${NC}: $description"
+        echo "  Pattern found but should not be: '$pattern'"
+        ((FAILED++))
+    fi
+}
+
+assert_count() {
+    local description="$1"
+    local expected="$2"
+    local pattern="$3"
+    local file="$4"
+
+    local actual
+    actual=$(grep -c "$pattern" "$file" 2>/dev/null || echo "0")
+
+    if [[ "$actual" == "$expected" ]]; then
+        echo -e "${GREEN}PASS${NC}: $description"
+        ((PASSED++))
+    else
+        echo -e "${RED}FAIL${NC}: $description"
+        echo "  Expected count: $expected, Actual: $actual"
+        echo "  Pattern: '$pattern'"
+        ((FAILED++))
+    fi
+}
+
+assert_last_line() {
+    local description="$1"
+    local expected="$2"
+    local file="$3"
+
+    local actual
+    actual=$(tail -n 1 "$file")
+
+    if [[ "$actual" == "$expected" ]]; then
+        echo -e "${GREEN}PASS${NC}: $description"
+        ((PASSED++))
+    else
+        echo -e "${RED}FAIL${NC}: $description"
+        echo "  Expected last line: '$expected'"
+        echo "  Actual last line: '$actual'"
+        ((FAILED++))
+    fi
+}
+
+assert_output_contains() {
+    local description="$1"
+    local pattern="$2"
+    local output="$3"
+
+    if echo "$output" | grep -q "$pattern"; then
+        echo -e "${GREEN}PASS${NC}: $description"
+        ((PASSED++))
+    else
+        echo -e "${RED}FAIL${NC}: $description"
+        echo "  Pattern not found: '$pattern'"
+        echo "  Output was: $output"
+        ((FAILED++))
+    fi
+}
+
+# Setup: create a minimal Nix file
+setup_nix_file() {
+    local content="$1"
+    local test_file
+    test_file=$(mktemp)
+    echo -e "$content" > "$test_file"
+    echo "$test_file"
+}
+
+cleanup() {
+    rm -f "$1"
+}
+
+echo "=== Deploy Skill Config Injection Tests ==="
+echo ""
+
+# --- Basic Injection ---
+echo "## Basic Injection"
+
+# Test: Config injected before closing brace
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+  home.packages = [ pkgs.git ];
+}")
+
+inject_nix_config "$test_file" "  # Added config
+  home.file.\"test\" = { source = ./test; };" "home.file.\"test\"" > /dev/null
+
+assert_contains "Config block injected" "home.file.\"test\"" "$test_file"
+assert_last_line "Closing brace preserved at end" "}" "$test_file"
+assert_contains "Original content preserved" "home.packages" "$test_file"
+
+cleanup "$test_file"
+
+# --- Idempotency ---
+echo ""
+echo "## Idempotency"
+
+# Test: Running twice doesn't duplicate
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+  home.packages = [ ];
+}")
+
+inject_nix_config "$test_file" "  home.file.\"skill-a\" = { source = ./a; };" "skill-a" > /dev/null
+inject_nix_config "$test_file" "  home.file.\"skill-a\" = { source = ./a; };" "skill-a" > /dev/null
+
+assert_count "Config not duplicated" "1" "skill-a" "$test_file"
+
+cleanup "$test_file"
+
+# Test: Different configs can be added
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+}")
+
+inject_nix_config "$test_file" "  home.file.\"skill-b\" = {};" "skill-b" > /dev/null
+inject_nix_config "$test_file" "  home.file.\"skill-c\" = {};" "skill-c" > /dev/null
+
+assert_contains "First config present" "skill-b" "$test_file"
+assert_contains "Second config present" "skill-c" "$test_file"
+assert_count "Each config appears once" "1" "skill-b" "$test_file"
+assert_count "Each config appears once (c)" "1" "skill-c" "$test_file"
+
+cleanup "$test_file"
+
+# --- File Not Found ---
+echo ""
+echo "## File Not Found Handling"
+
+output=$(inject_nix_config "/nonexistent/path/file.nix" "config" "marker" 2>&1)
+assert_output_contains "Skips missing file gracefully" "skipping" "$output"
+
+# --- Brace Structure ---
+echo ""
+echo "## Brace Structure Preservation"
+
+# Test: Complex nested structure
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+  programs.git = {
+    enable = true;
+    userName = \"test\";
+  };
+
+  home.packages = with pkgs; [
+    ripgrep
+    fd
+  ];
+}")
+
+inject_nix_config "$test_file" "
+  # New skill
+  home.file.\".skill\" = {
+    source = ./skill;
+    recursive = true;
+  };" ".skill" > /dev/null
+
+assert_last_line "Closing brace still at end after complex inject" "}" "$test_file"
+assert_contains "Nested braces preserved" "programs.git" "$test_file"
+assert_contains "New config added" ".skill" "$test_file"
+
+cleanup "$test_file"
+
+# --- inject_home_file Wrapper ---
+echo ""
+echo "## inject_home_file Wrapper"
+
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+}")
+
+inject_home_file "$test_file" \
+    ".claude/skills/my-skill" \
+    "../claude/skills/my-skill" \
+    "recursive = true;" \
+    "my-skill" > /dev/null
+
+assert_contains "Home path in config" ".claude/skills/my-skill" "$test_file"
+assert_contains "Source path in config" "../claude/skills/my-skill" "$test_file"
+assert_contains "Extra props included" "recursive = true" "$test_file"
+assert_contains "Comment included" "# Skill: my-skill" "$test_file"
+
+cleanup "$test_file"
+
+# Test: inject_home_file idempotency
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+}")
+
+inject_home_file "$test_file" ".test/path" "./source" "" "test" > /dev/null
+inject_home_file "$test_file" ".test/path" "./source" "" "test" > /dev/null
+
+assert_count "inject_home_file idempotent" "1" ".test/path" "$test_file"
+
+cleanup "$test_file"
+
+# --- Already Present Detection ---
+echo ""
+echo "## Already Present Detection"
+
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+  # Existing skill
+  home.file.\".claude/skills/existing\" = {
+    source = ./existing;
+  };
+}")
+
+output=$(inject_nix_config "$test_file" "new config" ".claude/skills/existing" 2>&1)
+assert_output_contains "Detects existing config" "already present" "$output"
+
+cleanup "$test_file"
+
+# --- Empty Extra Props ---
+echo ""
+echo "## Edge Cases"
+
+# Test: Empty extra props
+test_file=$(setup_nix_file "{ config, pkgs, ... }:
+{
+}")
+
+inject_home_file "$test_file" ".simple/path" "./src" "" "simple" > /dev/null
+
+assert_contains "Works with empty extra props" ".simple/path" "$test_file"
+
+cleanup "$test_file"
+
+# Test: Single line file (edge case - script assumes multi-line)
+test_file=$(setup_nix_file "{}")
+
+inject_nix_config "$test_file" "  config = true;" "config" > /dev/null
+
+assert_contains "Works with minimal file" "config = true" "$test_file"
+# Note: Single-line "{}" becomes last line since head -n -1 returns empty
+# This is acceptable - real Nix files are always multi-line
+assert_last_line "Original content preserved as last line" "{}" "$test_file"
+
+cleanup "$test_file"
+
+# --- Summary ---
+echo ""
+echo "=== Summary ==="
+echo -e "Passed: ${GREEN}$PASSED${NC}"
+echo -e "Failed: ${RED}$FAILED${NC}"
+
+if [[ $FAILED -gt 0 ]]; then
+    exit 1
+fi