diff --git a/packages/bugc/src/evmgen/behavioral.test.ts b/packages/bugc/src/evmgen/behavioral.test.ts
new file mode 100644
index 000000000..18c10db35
--- /dev/null
+++ b/packages/bugc/src/evmgen/behavioral.test.ts
@@ -0,0 +1,229 @@
+import { describe, it, expect } from "vitest";
+
+import { executeProgram } from "#test/evm/behavioral";
+
+describe("behavioral tests", () => {
+  describe("deploy + check storage", () => {
+    it("should initialize storage in constructor", async () => {
+      const source = `name InitStorage;
+
+storage {
+  [0] value: uint256;
+  [1] flag: uint256;
+}
+
+create {
+  value = 42;
+  flag = 1;
+}
+
+code {}`;
+
+      const result = await executeProgram(source);
+      expect(result.deployed).toBe(true);
+      expect(await result.getStorage(0n)).toBe(42n);
+      expect(await result.getStorage(1n)).toBe(1n);
+    });
+
+    it("should handle multiple storage slots", async () => {
+      const source = `name MultiSlot;
+
+storage {
+  [0] a: uint256;
+  [1] b: uint256;
+  [2] c: uint256;
+}
+
+create {
+  a = 100;
+  b = 200;
+  c = a + b;
+}
+
+code {}`;
+
+      const result = await executeProgram(source);
+      expect(await result.getStorage(0n)).toBe(100n);
+      expect(await result.getStorage(1n)).toBe(200n);
+      expect(await result.getStorage(2n)).toBe(300n);
+    });
+  });
+
+  describe("deploy + call + check storage", () => {
+    it("should modify storage on call", async () => {
+      const source = `name Counter;
+
+storage {
+  [0] count: uint256;
+}
+
+create {
+  count = 0;
+}
+
+code {
+  count = count + 1;
+}`;
+
+      const result = await executeProgram(source, {
+        calldata: "",
+      });
+
+      expect(result.callSuccess).toBe(true);
+      expect(await result.getStorage(0n)).toBe(1n);
+    });
+
+    it("should support multiple calls", async () => {
+      const source = `name MultiCall;
+
+storage {
+  [0] count: uint256;
+}
+
+create {
+  count = 0;
+}
+
+code {
+  count = count + 1;
+}`;
+
+      const result = await executeProgram(source, {
+        calldata: "",
+      });
+      expect(await result.getStorage(0n)).toBe(1n);
+
+      const execResult = await result.executor.execute({
+        data: "",
+      });
+      expect(execResult.success).toBe(true);
+      expect(await result.getStorage(0n)).toBe(2n);
+    });
+  });
+
+  describe("internal functions", () => {
+    // Internal function calls currently fail at runtime
+    // (stack underflow). Tracked as known issue.
+    it.skip("should call defined functions", async () => {
+      const source = `name FuncCall;
+
+define {
+  function add(a: uint256, b: uint256) -> uint256 {
+    return a + b;
+  };
+}
+
+storage {
+  [0] result: uint256;
+}
+
+create {
+  result = 0;
+}
+
+code {
+  result = add(10, 20);
+}`;
+
+      const result = await executeProgram(source, {
+        calldata: "",
+      });
+
+      expect(result.callSuccess).toBe(true);
+      expect(await result.getStorage(0n)).toBe(30n);
+    });
+  });
+
+  describe("loops", () => {
+    it("should execute a for loop", async () => {
+      const source = `name Loop;
+
+storage {
+  [0] total: uint256;
+}
+
+create {
+  total = 0;
+}
+
+code {
+  for (let i = 0; i < 5; i = i + 1) {
+    total = total + 1;
+  }
+}`;
+
+      const result = await executeProgram(source, {
+        calldata: "",
+      });
+
+      expect(result.callSuccess).toBe(true);
+      expect(await result.getStorage(0n)).toBe(5n);
+    });
+  });
+
+  describe("conditional behavior", () => {
+    it("should execute conditional branches", async () => {
+      const source = `name Conditional;
+
+storage {
+  [0] value: uint256;
+  [1] flag: uint256;
+}
+
+create {
+  value = 0;
+  flag = 1;
+}
+
+code {
+  if (flag == 1) {
+    value = 100;
+  } else {
+    value = 200;
+  }
+}`;
+
+      const result = await executeProgram(source, {
+        calldata: "",
+      });
+
+      expect(result.callSuccess).toBe(true);
+      expect(await result.getStorage(0n)).toBe(100n);
+    });
+  });
+
+  describe("error paths", () => {
+    it("should report compilation failure", async () => {
+      const source = `this is not valid BUG code`;
+
+      await expect(executeProgram(source)).rejects.toThrow(
+        /Compilation failed/,
+      );
+    });
+
+    it("should handle bare return (STOP)", async () => {
+      const source = `name EarlyReturn;
+
+storage {
+  [0] reached: uint256;
+}
+
+create {
+  reached = 0;
+}
+
+code {
+  reached = 1;
+  return;
+}`;
+
+      const result = await executeProgram(source, {
+        calldata: "",
+      });
+
+      expect(result.callSuccess).toBe(true);
+      expect(await result.getStorage(0n)).toBe(1n);
+      expect(result.returnValue.length).toBe(0);
+    });
+  });
+});
diff --git a/packages/bugc/test/evm/behavioral.ts b/packages/bugc/test/evm/behavioral.ts
new file mode 100644
index 000000000..33371e29f
--- /dev/null
+++ b/packages/bugc/test/evm/behavioral.ts
@@ -0,0 +1,68 @@
+import { compile } from "#compiler";
+import { Executor } from "@ethdebug/evm";
+import { bytesToHex } from "ethereum-cryptography/utils";
+
+export interface ExecuteProgramOptions {
+  calldata?: string;
+  value?: bigint;
+  optimizationLevel?: 0 | 1 | 2 | 3;
+}
+
+export interface ExecuteProgramResult {
+  deployed: boolean;
+  callSuccess?: boolean;
+  returnValue: Uint8Array;
+  getStorage: (slot: bigint) => Promise<bigint>;
+  executor: Executor;
+}
+
+export async function executeProgram(
+  source: string,
+  options: ExecuteProgramOptions = {},
+): Promise<ExecuteProgramResult> {
+  const { calldata, value, optimizationLevel = 0 } = options;
+
+  const result = await compile({
+    to: "bytecode",
+    source,
+    optimizer: { level: optimizationLevel },
+  });
+
+  if (!result.success) {
+    const errors = result.messages.error ?? [];
+    const msgs = errors
+      .map((e: { message?: string }) => e.message ?? String(e))
+      .join("\n");
+    throw new Error(`Compilation failed:\n${msgs}`);
+  }
+
+  const { bytecode } = result.value;
+  const executor = new Executor();
+
+  const hasCreate = bytecode.create && bytecode.create.length > 0;
+  const createCode = hasCreate
+    ? bytesToHex(bytecode.create!)
+    : bytesToHex(bytecode.runtime);
+
+  await executor.deploy(createCode);
+
+  let callSuccess: boolean | undefined;
+  let returnValue: Uint8Array = new Uint8Array();
+
+  if (calldata !== undefined) {
+    const execResult = await executor.execute({
+      data: calldata,
+      value,
+    });
+    callSuccess = execResult.success;
+    returnValue = new Uint8Array(execResult.returnValue);
+  }
+
+  return {
+    deployed: true,
+    callSuccess,
+    returnValue,
+    getStorage: (slot: bigint) => executor.getStorage(slot),
+    executor,
+  };
+}