diff --git a/tests/integration/import_test.nix b/tests/integration/import_test.nix
new file mode 100644
index 0000000..7914eea
--- /dev/null
+++ b/tests/integration/import_test.nix
@@ -0,0 +1,7 @@
+# Test that import builtin still works
+let
+  imported = import ./imported_module.nix;
+in {
+  value = imported.foo + 100;
+  nested = imported.bar.baz;
+}
diff --git a/tests/integration/imported_module.nix b/tests/integration/imported_module.nix
new file mode 100644
index 0000000..a9b969c
--- /dev/null
+++ b/tests/integration/imported_module.nix
@@ -0,0 +1,7 @@
+# Module to be imported
+{
+  foo = 42;
+  bar = {
+    baz = "hello";
+  };
+}
diff --git a/tests/integration/ir_builtins_test.nix b/tests/integration/ir_builtins_test.nix
new file mode 100644
index 0000000..4aa28e3
--- /dev/null
+++ b/tests/integration/ir_builtins_test.nix
@@ -0,0 +1,13 @@
+# Test our custom IR builtins
+let
+  # Test nixIR_info
+  info = builtins.nixIR_info;
+
+  # Test nixIR_compile
+  compiled = builtins.nixIR_compile "let x = 10; in x + 5";
+
+  # Test that normal builtins still work
+  list = builtins.map (x: x * 2) [1 2 3];
+in {
+  inherit info compiled list;
+}
diff --git a/tests/integration/regression_normal_nix.nix b/tests/integration/regression_normal_nix.nix
new file mode 100644
index 0000000..2eb73f6
--- /dev/null
+++ b/tests/integration/regression_normal_nix.nix
@@ -0,0 +1,39 @@
+# Test that normal Nix evaluation is not broken
+# This file should work identically with or without the plugin
+let
+  # Basic arithmetic
+  math = 1 + 2 * 3;
+
+  # String operations
+  str = "hello" + " " + "world";
+
+  # List operations
+  list = [1 2 3] ++ [4 5 6];
+
+  # Attrset operations
+  attrs =
+    {
+      a = 1;
+      b = 2;
+    }
+    // {c = 3;};
+
+  # Functions
+  double = x: x * 2;
+  result = double 21;
+
+  # Conditionals
+  cond =
+    if true
+    then "yes"
+    else "no";
+
+  # Let bindings
+  nested = let
+    x = 10;
+    y = 20;
+  in
+    x + y;
+in {
+  inherit math str list attrs result cond nested;
+}
diff --git a/tests/integration/run.sh b/tests/integration/run.sh
new file mode 100755
index 0000000..8645388
--- /dev/null
+++ b/tests/integration/run.sh
@@ -0,0 +1,76 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+echo "=== Phase 6: Integration Testing ==="
+echo ""
+
+PLUGIN_PATH="$(pwd)/build/nix-ir-plugin.so"
+TEST_DIR="$(pwd)/tests/integration"
+
+if [ ! -f "$PLUGIN_PATH" ]; then
+	echo "ERROR: Plugin not found at $PLUGIN_PATH"
+	exit 1
+fi
+
+echo "Plugin path: $PLUGIN_PATH"
+echo ""
+
+echo "Test 1: Plugin Loading"
+echo "----------------------"
+if nix-instantiate --plugin-files "$PLUGIN_PATH" --eval "$TEST_DIR/simple_eval.nix" 2>&1 | grep -q "30"; then
+	echo "[PASS] Plugin loads and evaluates correctly"
+else
+	echo "[FAIL] Plugin failed to load or evaluate"
+	exit 1
+fi
+echo ""
+
+echo "Test 2: Normal Nix Evaluation (No Plugin)"
+echo "------------------------------------------"
+result=$(nix-instantiate --eval --strict --json "$TEST_DIR/regression_normal_nix.nix" 2>&1)
+if echo "$result" | grep -q '"math":7'; then
+	echo "[PASS] Normal Nix evaluation works without plugin"
+else
+	echo "[FAIL] Normal Nix evaluation broken"
+	echo "$result"
+	exit 1
+fi
+echo ""
+
+echo "Test 3: Normal Nix Evaluation (With Plugin)"
+echo "--------------------------------------------"
+result=$(nix-instantiate --plugin-files "$PLUGIN_PATH" --eval --strict --json "$TEST_DIR/regression_normal_nix.nix" 2>&1)
+if echo "$result" | grep -q '"math":7'; then
+	echo "[PASS] Normal Nix evaluation works with plugin loaded"
+else
+	echo "[FAIL] Plugin breaks normal Nix evaluation"
+	echo "$result"
+	exit 1
+fi
+echo ""
+
+echo "Test 4: Import Builtin"
+echo "----------------------"
+cd "$TEST_DIR"
+result=$(nix-instantiate --plugin-files "$PLUGIN_PATH" --eval --strict --json import_test.nix 2>&1)
+if echo "$result" | grep -q '"value":142'; then
+	echo "[PASS] Import builtin works correctly"
+else
+	echo "[FAIL] Import builtin broken"
+	echo "$result"
+	exit 1
+fi
+cd - >/dev/null
+echo ""
+
+echo "Test 5: IR Builtins Available"
+echo "------------------------------"
+result=$(nix-instantiate --plugin-files "$PLUGIN_PATH" --eval "$TEST_DIR/ir_builtins_test.nix" 2>&1)
+if echo "$result" | grep -q "info.*="; then
+	echo "[PASS] IR builtins (nixIR_info, nixIR_compile, nixIR_loadIR) available"
+else
+	echo "[WARN] IR builtins may not be available (check plugin initialization)"
+fi
+echo ""
+
+echo "Integration Tests Complete"
diff --git a/tests/integration/simple_eval.nix b/tests/integration/simple_eval.nix
new file mode 100644
index 0000000..9dc2744
--- /dev/null
+++ b/tests/integration/simple_eval.nix
@@ -0,0 +1,6 @@
+# Simple expression to test plugin loading
+let
+  x = 10;
+  y = 20;
+in
+  x + y