diff --git a/src/tests/pushNotificationUtils.test.ts b/src/tests/pushNotificationUtils.test.ts
new file mode 100644
index 0000000..8f96936
--- /dev/null
+++ b/src/tests/pushNotificationUtils.test.ts
@@ -0,0 +1,536 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { StringUtils } from "../utils/stringUtils";
+
+// Mock environment variables for testing
+const originalEnv = process.env;
+
+beforeEach(() => {
+  vi.resetModules();
+  process.env = {
+    ...originalEnv,
+    APNS_P8: "2d2d2d2d2d424547494e205052495641544520534d454420454d454d454d454d20504f494e54452d2d2d2d2d0a4d484943416741472d412b6742414d42",
+    APPLE_TEAM_ID: "ABCD123456",
+    APNS_P8_KID: "ABC123DEF4",
+    GOOGLE_KEY_FILE: "7b2274797065223a22736572766963655f6163636f756e74222c2270726f6a6563745f6964223a2274657374227d",
+    GOOGLE_PROJECT_ID: "test-project-123",
+    APNS_TOPIC: "com.test.app",
+  };
+});
+
+afterEach(() => {
+  process.env = originalEnv;
+  vi.restoreAllMocks();
+});
+
+describe("Push Notification System", () => {
+  describe("StringUtils", () => {
+    describe("shortenAddress", () => {
+      it("should shorten Bitcoin addresses correctly", () => {
+        const longAddress = "bc1qxy2kgdygjrsqtzq2n0yrf2493p83kkfjhx0wlh";
+        const result = StringUtils.shortenAddress(longAddress);
+        expect(result).toBe("bc1qx....0wlh");
+      });
+
+      it("should shorten Lightning addresses correctly", () => {
+        const lightningAddress = "1MNH5eZ1AFZGhBg5FjNt35H7YfZE1AW8Zf";
+        const result = StringUtils.shortenAddress(lightningAddress);
+        expect(result).toBe("1MNH5....W8Zf");
+      });
+
+      it("should handle bech32 addresses", () => {
+        const bech32Address = "bc1qrnn4wfhgz2e0etek66sh3n9l6k99alxk044mhr";
+        const result = StringUtils.shortenAddress(bech32Address);
+        expect(result).toBe("bc1qr....4mhr");
+      });
+
+      it("should handle legacy addresses", () => {
+        const legacyAddress = "1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa";
+        const result = StringUtils.shortenAddress(legacyAddress);
+        expect(result).toBe("1A1zP....vfNa");
+      });
+
+      it("should handle Taproot addresses", () => {
+        const taprootAddress = "bc1pmfr3p9j00pfxjh0zmgp99y8zftmd3s5pmedqhyptwy6lm87hf5sspknykm";
+        const result = StringUtils.shortenAddress(taprootAddress);
+        expect(result).toBe("bc1pm....nykm");
+      });
+
+      it("should return unchanged for very short addresses", () => {
+        const shortAddress = "short";
+        const result = StringUtils.shortenAddress(shortAddress);
+        expect(result).toBe("short");
+      });
+
+      it("should handle exactly 10 character strings", () => {
+        const tenCharAddress = "1234567890";
+        const result = StringUtils.shortenAddress(tenCharAddress);
+        expect(result).toBe("12345....7890");
+      });
+
+      it("should handle empty strings gracefully", () => {
+        const emptyAddress = "";
+        const result = StringUtils.shortenAddress(emptyAddress);
+        expect(result).toBe("");
+      });
+
+      it("should handle null and undefined safely", () => {
+        // The current implementation doesn't handle null/undefined, so we expect errors
+        expect(() => StringUtils.shortenAddress(null as any)).toThrow();
+        expect(() => StringUtils.shortenAddress(undefined as any)).toThrow();
+      });
+
+      it("should handle special characters in addresses", () => {
+        const specialAddress = "abc!@#$%^&*()def1234567890";
+        const result = StringUtils.shortenAddress(specialAddress);
+        expect(result).toBe("abc!@....7890");
+      });
+    });
+
+    describe("shortenTxid", () => {
+      it("should shorten transaction IDs correctly", () => {
+        const longTxid = "a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456";
+        const result = StringUtils.shortenTxid(longTxid);
+        expect(result).toBe("a1b2c....3456");
+      });
+
+      it("should match shortenAddress behavior exactly", () => {
+        const txid = "f2ca1bb6c7e907d06dafe4687cf0c76f0b8c33d6c7e907d06dafe4687cf0c76f";
+        const addressResult = StringUtils.shortenAddress(txid);
+        const txidResult = StringUtils.shortenTxid(txid);
+        expect(addressResult).toBe(txidResult);
+      });
+
+      it("should handle Lightning invoice payment hashes", () => {
+        const hash = "abcdef123456789012345678901234567890abcdef123456789012345678901234";
+        const result = StringUtils.shortenTxid(hash);
+        expect(result).toBe("abcde....1234");
+      });
+
+      it("should handle shorter transaction IDs", () => {
+        const shortTxid = "abc123";
+        const result = StringUtils.shortenTxid(shortTxid);
+        expect(result).toBe("abc123");
+      });
+    });
+  });
+
+  describe("Push Notification Payload Generation", () => {
+    let mockFcmPayload: any;
+    let mockApnsPayload: any;
+
+    beforeEach(() => {
+      mockFcmPayload = {
+        message: {
+          token: "",
+          data: {},
+          notification: {},
+        },
+      };
+
+      mockApnsPayload = {
+        aps: {
+          badge: 0,
+          alert: {},
+          sound: "default",
+        },
+        data: {},
+      };
+    });
+
+    describe("Bitcoin Transaction Notifications", () => {
+      it("should create correct unconfirmed transaction payload", () => {
+        const address = "bc1qxy2kgdygjrsqtzq2n0yrf2493p83kkfjhx0wlh";
+        const txid = "a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456";
+        const badge = 5;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.data.badge = String(badge);
+        mockFcmPayload.message.data.tag = txid;
+        mockFcmPayload.message.notification.title = "New unconfirmed transaction";
+        mockFcmPayload.message.notification.body = "You received new transfer on " + StringUtils.shortenAddress(address);
+
+        expect(mockFcmPayload.message.notification.title).toBe("New unconfirmed transaction");
+        expect(mockFcmPayload.message.notification.body).toBe("You received new transfer on bc1qx....0wlh");
+        expect(mockFcmPayload.message.data.badge).toBe("5");
+        expect(mockFcmPayload.message.data.tag).toBe(txid);
+      });
+
+      it("should create correct confirmed payment payload", () => {
+        const address = "bc1qxy2kgdygjrsqtzq2n0yrf2493p83kkfjhx0wlh";
+        const txid = "a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456";
+        const satAmount = 50000;
+        const badge = 3;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.data.badge = String(badge);
+        mockFcmPayload.message.data.tag = txid;
+        mockFcmPayload.message.notification.title = "+" + satAmount + " sats";
+        mockFcmPayload.message.notification.body = "Received on " + StringUtils.shortenAddress(address);
+
+        expect(mockFcmPayload.message.notification.title).toBe("+50000 sats");
+        expect(mockFcmPayload.message.notification.body).toBe("Received on bc1qx....0wlh");
+        expect(mockFcmPayload.message.data.badge).toBe("3");
+      });
+
+      it("should create correct transaction confirmation payload", () => {
+        const txid = "a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456";
+        const badge = 2;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.data.badge = String(badge);
+        mockFcmPayload.message.data.tag = txid;
+        mockFcmPayload.message.notification.title = "Transaction - Confirmed";
+        mockFcmPayload.message.notification.body = "Your transaction " + StringUtils.shortenTxid(txid) + " has been confirmed";
+
+        expect(mockFcmPayload.message.notification.title).toBe("Transaction - Confirmed");
+        expect(mockFcmPayload.message.notification.body).toBe("Your transaction a1b2c....3456 has been confirmed");
+        expect(mockFcmPayload.message.data.tag).toBe(txid);
+      });
+    });
+
+    describe("Lightning Network Notifications", () => {
+      it("should create correct lightning invoice paid payload with memo", () => {
+        const satAmount = 1000;
+        const memo = "Coffee payment";
+        const hash = "abcdef123456789012345678901234567890abcdef123456789012345678901234";
+        const badge = 1;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.data.badge = String(badge);
+        mockFcmPayload.message.data.tag = hash;
+        mockFcmPayload.message.notification.title = "+" + satAmount + " sats";
+        mockFcmPayload.message.notification.body = "Paid: " + (memo || "your invoice");
+
+        expect(mockFcmPayload.message.notification.title).toBe("+1000 sats");
+        expect(mockFcmPayload.message.notification.body).toBe("Paid: Coffee payment");
+        expect(mockFcmPayload.message.data.tag).toBe(hash);
+      });
+
+      it("should handle missing memo gracefully", () => {
+        const satAmount = 1000;
+        const memo = undefined;
+        const badge = 1;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.data.badge = String(badge);
+        mockFcmPayload.message.notification.title = "+" + satAmount + " sats";
+        mockFcmPayload.message.notification.body = "Paid: " + (memo || "your invoice");
+
+        expect(mockFcmPayload.message.notification.body).toBe("Paid: your invoice");
+      });
+
+      it("should handle empty memo correctly", () => {
+        const satAmount = 1000;
+        const memo = "";
+        const badge = 1;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.data.badge = String(badge);
+        mockFcmPayload.message.notification.title = "+" + satAmount + " sats";
+        mockFcmPayload.message.notification.body = "Paid: " + (memo || "your invoice");
+
+        expect(mockFcmPayload.message.notification.body).toBe("Paid: your invoice");
+      });
+
+      it("should handle large lightning payments", () => {
+        const satAmount = 100000000; // 1 BTC in sats
+        const memo = "Large payment";
+        const badge = 1;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.notification.title = "+" + satAmount + " sats";
+        mockFcmPayload.message.notification.body = "Paid: " + memo;
+
+        expect(mockFcmPayload.message.notification.title).toBe("+100000000 sats");
+        expect(mockFcmPayload.message.notification.body).toBe("Paid: Large payment");
+      });
+    });
+
+    describe("Generic Message Notifications", () => {
+      it("should create simple message notification", () => {
+        const text = "Welcome to GroundControl!";
+        const badge = 2;
+
+        // Simulate FCM payload creation
+        mockFcmPayload.message.data = {};
+        mockFcmPayload.message.notification.title = "Message";
+        mockFcmPayload.message.notification.body = text;
+
+        expect(mockFcmPayload.message.notification.title).toBe("Message");
+        expect(mockFcmPayload.message.notification.body).toBe("Welcome to GroundControl!");
+      });
+
+      it("should handle long messages", () => {
+        const longText = "This is a very long message that might be truncated depending on the push notification service limits. It contains important information that users need to see.";
+        
+        // Simulate FCM payload creation
+        mockFcmPayload.message.notification.title = "Message";
+        mockFcmPayload.message.notification.body = longText;
+
+        expect(mockFcmPayload.message.notification.body).toBe(longText);
+        expect(mockFcmPayload.message.notification.body.length).toBeGreaterThan(100);
+      });
+
+      it("should handle special characters in messages", () => {
+        const specialText = "Message with émojis 🚀 and special chars: &<>\"'";
+        
+        // Simulate FCM payload creation
+        mockFcmPayload.message.notification.title = "Message";
+        mockFcmPayload.message.notification.body = specialText;
+
+        expect(mockFcmPayload.message.notification.body).toBe(specialText);
+      });
+    });
+
+    describe("APNS vs FCM Payload Differences", () => {
+      it("should format badges differently for FCM vs APNS", () => {
+        const badge = 5;
+
+        // FCM uses string badges
+        mockFcmPayload.message.data.badge = String(badge);
+        
+        // APNS uses numeric badges
+        mockApnsPayload.aps.badge = badge;
+
+        expect(mockFcmPayload.message.data.badge).toBe("5");
+        expect(mockApnsPayload.aps.badge).toBe(5);
+        expect(typeof mockFcmPayload.message.data.badge).toBe("string");
+        expect(typeof mockApnsPayload.aps.badge).toBe("number");
+      });
+
+      it("should structure alert content differently", () => {
+        const title = "New Payment";
+        const body = "You received 1000 sats";
+
+        // FCM structure
+        mockFcmPayload.message.notification = { title, body };
+        
+        // APNS structure
+        mockApnsPayload.aps.alert = { title, body };
+
+        expect(mockFcmPayload.message.notification.title).toBe(title);
+        expect(mockFcmPayload.message.notification.body).toBe(body);
+        expect(mockApnsPayload.aps.alert.title).toBe(title);
+        expect(mockApnsPayload.aps.alert.body).toBe(body);
+      });
+
+      it("should include default sound for APNS", () => {
+        expect(mockApnsPayload.aps.sound).toBe("default");
+        expect(mockFcmPayload.message.sound).toBeUndefined();
+      });
+    });
+  });
+
+  describe("Response Processing Logic", () => {
+    describe("FCM Response Processing", () => {
+      it("should identify successful FCM responses", () => {
+        const successfulResponses = [
+          '{"name": "projects/test/messages/123"}',
+          '{"name": "projects/test/messages/456", "messageId": "abc"}',
+        ];
+
+        successfulResponses.forEach(response => {
+          const parsed = JSON.parse(response);
+          const isSuccess = !!parsed.name;
+          expect(isSuccess).toBe(true);
+        });
+      });
+
+      it("should identify token-killing FCM errors", () => {
+        const tokenKillingErrors = [
+          '{"error": {"code": 404, "message": "Not found"}}',
+          '{"error": {"details": [{"errorCode": "UNREGISTERED"}]}}',
+        ];
+
+        tokenKillingErrors.forEach(errorResponse => {
+          const parsed = JSON.parse(errorResponse);
+          const shouldKillToken = 
+            (parsed.error?.code === 404) ||
+            (Array.isArray(parsed.error?.details) && 
+             parsed.error.details.some((d: any) => d.errorCode === "UNREGISTERED"));
+          
+          expect(shouldKillToken).toBe(true);
+        });
+      });
+
+      it("should handle non-token-killing FCM errors", () => {
+        const nonKillingErrors = [
+          '{"error": {"code": 500, "message": "Internal error"}}',
+          '{"error": {"code": 429, "message": "Rate limited"}}',
+          '{"error": {"code": 400, "message": "Invalid request"}}',
+        ];
+
+        nonKillingErrors.forEach(errorResponse => {
+          const parsed = JSON.parse(errorResponse);
+          const shouldKillToken = parsed.error?.code === 404;
+          expect(shouldKillToken).toBe(false);
+        });
+      });
+
+      it("should handle malformed JSON responses", () => {
+        const malformedResponses = [
+          '{"invalid": json}',
+          'not json at all',
+          '',
+          '{incomplete',
+        ];
+
+        malformedResponses.forEach(response => {
+          let isValidJson = true;
+          try {
+            JSON.parse(response);
+          } catch {
+            isValidJson = false;
+          }
+          expect(isValidJson).toBe(false);
+        });
+      });
+    });
+
+    describe("APNS Response Processing", () => {
+      it("should identify token-killing APNS reasons", () => {
+        const tokenKillingReasons = [
+          "Unregistered",
+          "BadDeviceToken", 
+          "DeviceTokenNotForTopic"
+        ];
+
+        tokenKillingReasons.forEach(reason => {
+          const response = { data: JSON.stringify({ reason }), ":status": 400 };
+          const parsed = JSON.parse(response.data);
+          const shouldKillToken = ["Unregistered", "BadDeviceToken", "DeviceTokenNotForTopic"].includes(parsed.reason);
+          expect(shouldKillToken).toBe(true);
+        });
+      });
+
+      it("should handle non-token-killing APNS reasons", () => {
+        const nonKillingReasons = [
+          "PayloadTooLarge",
+          "BadCertificate",
+          "BadPath",
+          "BadCertificateEnvironment"
+        ];
+
+        nonKillingReasons.forEach(reason => {
+          const response = { data: JSON.stringify({ reason }), ":status": 400 };
+          const parsed = JSON.parse(response.data);
+          const shouldKillToken = ["Unregistered", "BadDeviceToken", "DeviceTokenNotForTopic"].includes(parsed.reason);
+          expect(shouldKillToken).toBe(false);
+        });
+      });
+
+      it("should handle successful APNS responses", () => {
+        const successfulResponse = { ":status": 200 };
+        expect(successfulResponse[":status"]).toBe(200);
+      });
+
+      it("should handle APNS responses without data", () => {
+        const responseWithoutData: any = { ":status": 400 };
+        expect(responseWithoutData.data).toBeUndefined();
+      });
+    });
+  });
+
+  describe("Data Validation and Edge Cases", () => {
+    describe("Address Validation", () => {
+      it("should handle various Bitcoin address formats", () => {
+        const addresses = [
+          "1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa", // Legacy
+          "3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy", // P2SH
+          "bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4", // Bech32
+          "bc1pmfr3p9j00pfxjh0zmgp99y8zftmd3s5pmedqhyptwy6lm87hf5sspknykm", // Taproot
+        ];
+
+        addresses.forEach(address => {
+          const shortened = StringUtils.shortenAddress(address);
+          expect(shortened).toContain("....");
+          expect(shortened.length).toBeLessThan(address.length);
+        });
+      });
+
+      it("should handle invalid addresses gracefully", () => {
+        const invalidAddresses = [
+          "invalid_address",
+          "bc1invalid",
+          "1invalid",
+          "3invalid",
+        ];
+
+        invalidAddresses.forEach(address => {
+          // StringUtils should still work even with invalid addresses
+          expect(() => StringUtils.shortenAddress(address)).not.toThrow();
+        });
+      });
+    });
+
+    describe("Satoshi Amount Handling", () => {
+      it("should handle various satoshi amounts", () => {
+        const amounts = [
+          1, // 1 sat
+          100, // 100 sats
+          1000, // 1k sats
+          100000, // 100k sats
+          100000000, // 1 BTC
+          2100000000000000, // Max Bitcoin supply
+        ];
+
+        amounts.forEach(amount => {
+          const title = "+" + amount + " sats";
+          expect(title).toMatch(/^\+\d+ sats$/);
+          expect(parseInt(title.replace(/^\+(\d+) sats$/, '$1'))).toBe(amount);
+        });
+      });
+
+      it("should handle zero and negative amounts", () => {
+        const zeroAmount = 0;
+        const title = "+" + zeroAmount + " sats";
+        expect(title).toBe("+0 sats");
+
+        // Negative amounts shouldn't happen in practice, but let's be safe
+        const negativeAmount = -100;
+        const negativeTitle = "+" + negativeAmount + " sats";
+        expect(negativeTitle).toBe("+-100 sats");
+      });
+    });
+
+    describe("Memo and Text Handling", () => {
+      it("should handle various memo formats", () => {
+        const memos = [
+          "Simple memo",
+          "Memo with émojis 🚀⚡",
+          "Memo with special chars: &<>\"'",
+          "Very long memo that goes on and on and might be truncated by some services",
+          "",
+          undefined,
+          null,
+        ];
+
+        memos.forEach(memo => {
+          const body = "Paid: " + (memo || "your invoice");
+          if (memo) {
+            expect(body).toBe(`Paid: ${memo}`);
+          } else {
+            expect(body).toBe("Paid: your invoice");
+          }
+        });
+      });
+
+      it("should handle unicode and special characters", () => {
+        const specialTexts = [
+          "Bitcoin ₿",
+          "Lightning ⚡",
+          "Japanese: こんにちは",
+          "Emoji: 🚀💰⚡₿",
+          "HTML: <script>alert('test')</script>",
+          "SQL: '; DROP TABLE users; --",
+        ];
+
+        specialTexts.forEach(text => {
+          // Text should be preserved as-is
+          const notification = { body: text };
+          expect(notification.body).toBe(text);
+        });
+      });
+    });
+  });
+});
\ No newline at end of file
diff --git a/vitest.config.mts b/vitest.config.mts
index 35d55ae..8e983bc 100644
--- a/vitest.config.mts
+++ b/vitest.config.mts
@@ -6,5 +6,6 @@ export default defineConfig({
     environment: "node",
     include: ["**/*.{test,spec}.{js,mjs,cjs,ts,mts,cts,jsx,tsx}"],
     exclude: ["node_modules", "dist", "build", ".git", ".github"],
+    setupFiles: ["reflect-metadata"],
   },
 });