diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 352ac57e..6e4294c5 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -1,6 +1,6 @@
 name: Build and Test
 
-on: [push, pull_request]
+on: [push]
 jobs: 
   build-and-test:
     name: build-and-test
diff --git a/coverage/lcov.info b/coverage/lcov.info
deleted file mode 100644
index 2dc2b01d..00000000
--- a/coverage/lcov.info
+++ /dev/null
@@ -1,1945 +0,0 @@
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diff --git a/lib/flutter_paystack.dart b/lib/flutter_paystack.dart
index 8eb88b02..346b001d 100644
--- a/lib/flutter_paystack.dart
+++ b/lib/flutter_paystack.dart
@@ -1,7 +1,7 @@
 // Expose the following files
-export 'package:flutter_paystack/src/model/card.dart';
+export 'package:flutter_paystack/src/common/exceptions.dart';
 export 'package:flutter_paystack/src/common/paystack.dart' hide Paystack;
+export 'package:flutter_paystack/src/model/card.dart';
 export 'package:flutter_paystack/src/model/charge.dart';
-export 'package:flutter_paystack/src/common/transaction.dart';
-export 'package:flutter_paystack/src/common/exceptions.dart';
 export 'package:flutter_paystack/src/model/checkout_response.dart';
+export 'package:flutter_paystack/src/model/transaction.dart';
diff --git a/lib/src/common/paystack.dart b/lib/src/common/paystack.dart
index 157bbcc8..e00b5e54 100644
--- a/lib/src/common/paystack.dart
+++ b/lib/src/common/paystack.dart
@@ -6,14 +6,15 @@ import 'package:flutter/services.dart';
 import 'package:flutter_paystack/src/common/exceptions.dart';
 import 'package:flutter_paystack/src/common/my_strings.dart';
 import 'package:flutter_paystack/src/common/platform_info.dart';
-import 'package:flutter_paystack/src/common/transaction.dart';
 import 'package:flutter_paystack/src/common/utils.dart';
 import 'package:flutter_paystack/src/model/card.dart';
 import 'package:flutter_paystack/src/model/charge.dart';
 import 'package:flutter_paystack/src/model/checkout_response.dart';
+import 'package:flutter_paystack/src/model/transaction.dart';
 import 'package:flutter_paystack/src/transaction/card_transaction_manager.dart';
 import 'package:flutter_paystack/src/widgets/checkout/checkout_widget.dart';
 
+// TODO: Remove use of static publicKey and use a constructor for initialization
 class PaystackPlugin {
   static bool _sdkInitialized = false;
   static String _publicKey;
@@ -68,6 +69,11 @@ class PaystackPlugin {
     }
   }
 
+  static dispose() {
+    _publicKey = null;
+    _sdkInitialized = false;
+  }
+
   static bool get sdkInitialized => _sdkInitialized;
 
   static String get publicKey {
@@ -79,9 +85,6 @@ class PaystackPlugin {
   static void _performChecks() {
     //validate that sdk has been initialized
     Utils.validateSdkInitialized();
-
-    //validate public keys
-    Utils.hasPublicKey();
   }
 
   /// Make payment by charging the user's card
diff --git a/lib/src/common/string_utils.dart b/lib/src/common/string_utils.dart
index 374f59ea..599af3d9 100644
--- a/lib/src/common/string_utils.dart
+++ b/lib/src/common/string_utils.dart
@@ -4,14 +4,8 @@ class StringUtils {
   }
 
   static bool isValidEmail(String email) {
-    String p = r"[a-zA-Z0-9\\+\\.\\_\\%\\-\\+]{1,256}" +
-        "\\@" +
-        "[a-zA-Z0-9][a-zA-Z0-9\\-]{0,64}" +
-        "(" +
-        "\\." +
-        "[a-zA-Z0-9][a-zA-Z0-9\\-]{0,25}" +
-        ")+";
-    RegExp regExp = new RegExp(p);
+    if (isEmpty(email)) return false;
+    RegExp regExp = new RegExp(_emailRegex);
     return regExp.hasMatch(email);
   }
 
@@ -25,3 +19,11 @@ class StringUtils {
     return value;
   }
 }
+
+const _emailRegex = r"[a-zA-Z0-9\\+\\.\\_\\%\\-\\+]{1,256}" +
+    "\\@" +
+    "[a-zA-Z0-9][a-zA-Z0-9\\-]{0,64}" +
+    "(" +
+    "\\." +
+    "[a-zA-Z0-9][a-zA-Z0-9\\-]{0,25}" +
+    ")+";
diff --git a/lib/src/common/utils.dart b/lib/src/common/utils.dart
index 464e84ea..2ae73613 100644
--- a/lib/src/common/utils.dart
+++ b/lib/src/common/utils.dart
@@ -5,6 +5,7 @@ import 'package:async/async.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_paystack/flutter_paystack.dart';
 import 'package:flutter_paystack/src/common/exceptions.dart';
+import 'package:flutter_paystack/src/common/string_utils.dart';
 import 'package:flutter_paystack/src/widgets/checkout/bank_checkout.dart';
 import 'package:http/http.dart' as http;
 import 'package:intl/intl.dart';
@@ -38,14 +39,6 @@ class Utils {
     }
   }
 
-  static hasPublicKey() {
-    var publicKey = PaystackPlugin.publicKey;
-    if (publicKey == null || publicKey.isEmpty) {
-      throw PaystackException(
-          'No Public key found, please set the Public key.');
-    }
-  }
-
   static String getKeyErrorMsg(String keyType) {
     return 'Invalid $keyType key. You must use a valid $keyType key. Ensure that you '
         'have set a $keyType key. Check http://paystack.co for more';
@@ -77,7 +70,7 @@ class Utils {
     if (charge.amount == null || charge.amount.isNegative) {
       throw new InvalidAmountException(charge.amount);
     }
-    if (charge.email == null || charge.email.isEmpty) {
+    if (!StringUtils.isValidEmail(charge.email)) {
       throw new InvalidEmailException(charge.email);
     }
   }
diff --git a/lib/src/model/charge.dart b/lib/src/model/charge.dart
index e4cf26fb..33cc3947 100644
--- a/lib/src/model/charge.dart
+++ b/lib/src/model/charge.dart
@@ -1,15 +1,18 @@
 import 'package:flutter_paystack/src/common/exceptions.dart';
 import 'package:flutter_paystack/src/common/my_strings.dart';
-import 'package:flutter_paystack/src/common/string_utils.dart';
 import 'package:flutter_paystack/src/model/card.dart';
 import 'package:flutter_paystack/src/widgets/checkout/bank_checkout.dart';
 
 class Charge {
   PaymentCard card;
-  String _email;
+
+  /// The email of the customer
+  String email;
   String _accessCode;
   BankAccount _account;
-  int _amount = 0;
+
+  /// Amount to pay in base currency. Must be a valid positive number
+  int amount = 0;
   Map<String, dynamic> _metadata;
   List<Map<String, dynamic>> _customFields;
   bool _hasMeta = false;
@@ -51,7 +54,7 @@ class Charge {
 
   Charge() {
     this._metadata = {};
-    this._amount = -1;
+    this.amount = -1;
     this._additionalParameters = {};
     this._customFields = [];
     this._metadata['custom_fields'] = this._customFields;
@@ -82,7 +85,9 @@ class Charge {
 
   String get currency => _currency;
 
-  /// ISO 4217 payment currency code (e.g USD). Defaults to [Strings.ngn]
+  /// ISO 4217 payment currency code (e.g USD). Defaults to [Strings.ngn].
+  ///
+  /// If you're setting this value, also set [locale] for better formatting.
   set currency(String value) {
     _beforeLocalSet('currency');
     _currency = value;
@@ -152,30 +157,6 @@ class Charge {
 
     return _metadata.toString();
   }
-
-  String get email => _email;
-
-  /// The email of the customer
-  set email(String value) {
-    // _beforeLocalSet('email');  Not needed because of PaystackPlugin.checkout. Email
-    // is needed for the checkout ui even after setting access code.
-    if (!StringUtils.isValidEmail(value)) {
-      throw InvalidEmailException(value);
-    }
-    _email = value;
-  }
-
-  int get amount => _amount;
-
-  /// Amount to pay in base currency. Must be a valid positive number
-  set amount(int value) {
-    // _beforeLocalSet('amount'); Not needed because of PaystackPlugin.checkout. Amount
-    // is needed for the checkout ui even after setting access code.
-    if (value <= 0) {
-      throw InvalidAmountException(value);
-    }
-    _amount = value;
-  }
 }
 
 enum Bearer {
diff --git a/lib/src/common/transaction.dart b/lib/src/model/transaction.dart
similarity index 100%
rename from lib/src/common/transaction.dart
rename to lib/src/model/transaction.dart
diff --git a/lib/src/transaction/bank_transaction_manager.dart b/lib/src/transaction/bank_transaction_manager.dart
index 8ee54a06..1b115430 100644
--- a/lib/src/transaction/bank_transaction_manager.dart
+++ b/lib/src/transaction/bank_transaction_manager.dart
@@ -6,9 +6,9 @@ import 'package:flutter_paystack/src/api/request/bank_charge_request_body.dart';
 import 'package:flutter_paystack/src/api/service/bank_service.dart';
 import 'package:flutter_paystack/src/common/exceptions.dart';
 import 'package:flutter_paystack/src/common/my_strings.dart';
-import 'package:flutter_paystack/src/model/charge.dart';
 import 'package:flutter_paystack/src/common/paystack.dart';
-import 'package:flutter_paystack/src/common/transaction.dart';
+import 'package:flutter_paystack/src/model/charge.dart';
+import 'package:flutter_paystack/src/model/transaction.dart';
 import 'package:flutter_paystack/src/transaction/base_transaction_manager.dart';
 
 class BankTransactionManager extends BaseTransactionManager {
diff --git a/lib/src/transaction/base_transaction_manager.dart b/lib/src/transaction/base_transaction_manager.dart
index 2e08dd06..6b109845 100644
--- a/lib/src/transaction/base_transaction_manager.dart
+++ b/lib/src/transaction/base_transaction_manager.dart
@@ -6,10 +6,10 @@ import 'package:flutter/material.dart';
 import 'package:flutter_paystack/src/api/model/transaction_api_response.dart';
 import 'package:flutter_paystack/src/common/exceptions.dart';
 import 'package:flutter_paystack/src/common/paystack.dart';
-import 'package:flutter_paystack/src/common/transaction.dart';
 import 'package:flutter_paystack/src/common/utils.dart';
 import 'package:flutter_paystack/src/model/card.dart';
 import 'package:flutter_paystack/src/model/charge.dart';
+import 'package:flutter_paystack/src/model/transaction.dart';
 import 'package:flutter_paystack/src/widgets/birthday_widget.dart';
 import 'package:flutter_paystack/src/widgets/card_widget.dart';
 import 'package:flutter_paystack/src/widgets/otp_widget.dart';
diff --git a/lib/src/transaction/card_transaction_manager.dart b/lib/src/transaction/card_transaction_manager.dart
index 6792bf4b..96103e0a 100644
--- a/lib/src/transaction/card_transaction_manager.dart
+++ b/lib/src/transaction/card_transaction_manager.dart
@@ -8,8 +8,8 @@ import 'package:flutter_paystack/src/api/service/card_service.dart';
 import 'package:flutter_paystack/src/common/exceptions.dart';
 import 'package:flutter_paystack/src/common/my_strings.dart';
 import 'package:flutter_paystack/src/common/paystack.dart';
-import 'package:flutter_paystack/src/common/transaction.dart';
 import 'package:flutter_paystack/src/model/charge.dart';
+import 'package:flutter_paystack/src/model/transaction.dart';
 import 'package:flutter_paystack/src/transaction/base_transaction_manager.dart';
 
 class CardTransactionManager extends BaseTransactionManager {
diff --git a/lib/src/widgets/checkout/bank_checkout.dart b/lib/src/widgets/checkout/bank_checkout.dart
index 40f470a0..ce05eb01 100644
--- a/lib/src/widgets/checkout/bank_checkout.dart
+++ b/lib/src/widgets/checkout/bank_checkout.dart
@@ -3,10 +3,10 @@ import 'dart:async';
 import 'package:async/async.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_paystack/src/common/paystack.dart';
-import 'package:flutter_paystack/src/common/transaction.dart';
 import 'package:flutter_paystack/src/common/utils.dart';
 import 'package:flutter_paystack/src/model/charge.dart';
 import 'package:flutter_paystack/src/model/checkout_response.dart';
+import 'package:flutter_paystack/src/model/transaction.dart';
 import 'package:flutter_paystack/src/transaction/bank_transaction_manager.dart';
 import 'package:flutter_paystack/src/widgets/buttons.dart';
 import 'package:flutter_paystack/src/widgets/checkout/base_checkout.dart';
diff --git a/lib/src/widgets/checkout/card_checkout.dart b/lib/src/widgets/checkout/card_checkout.dart
index 80a5eabb..35caafaa 100644
--- a/lib/src/widgets/checkout/card_checkout.dart
+++ b/lib/src/widgets/checkout/card_checkout.dart
@@ -2,11 +2,11 @@ import 'package:flutter/material.dart';
 import 'package:flutter_paystack/src/common/exceptions.dart';
 import 'package:flutter_paystack/src/common/my_strings.dart';
 import 'package:flutter_paystack/src/common/paystack.dart';
-import 'package:flutter_paystack/src/common/transaction.dart';
 import 'package:flutter_paystack/src/common/utils.dart';
 import 'package:flutter_paystack/src/model/card.dart';
 import 'package:flutter_paystack/src/model/charge.dart';
 import 'package:flutter_paystack/src/model/checkout_response.dart';
+import 'package:flutter_paystack/src/model/transaction.dart';
 import 'package:flutter_paystack/src/transaction/card_transaction_manager.dart';
 import 'package:flutter_paystack/src/widgets/checkout/base_checkout.dart';
 import 'package:flutter_paystack/src/widgets/checkout/checkout_widget.dart';
diff --git a/test/src/common/cart_utils_test.dart b/test/src/common/card_utils_test.dart
similarity index 50%
rename from test/src/common/cart_utils_test.dart
rename to test/src/common/card_utils_test.dart
index a88ec467..e8e4c7c4 100644
--- a/test/src/common/cart_utils_test.dart
+++ b/test/src/common/card_utils_test.dart
@@ -2,22 +2,23 @@ import 'package:flutter_paystack/flutter_paystack.dart';
 import 'package:flutter_paystack/src/common/card_utils.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:matcher/matcher.dart';
-import 'package:meta/meta.dart';
+
+import 'case.dart';
 
 void main() {
   group("$CardUtils", () {
     group("#isWholeNumberPositive", () {
       final cases = [
-        _Case(inp: "12", out: true),
-        _Case(inp: "+9876567", out: false),
-        _Case(inp: "hgfdfghjk", out: false),
-        _Case(inp: "KDHJIWUHE", out: false),
-        _Case(inp: "-1-2-84ufpo", out: false),
-        _Case(inp: "一些角色", out: false),
-        _Case(inp: "九十", out: false),
-        _Case(inp: "девяносто", out: false),
-        _Case(inp: "09765678987656789876545678987656789876545678", out: true),
-        _Case(inp: null, out: false),
+        Case(inp: "12", out: true),
+        Case(inp: "+9876567", out: false),
+        Case(inp: "hgfdfghjk", out: false),
+        Case(inp: "KDHJIWUHE", out: false),
+        Case(inp: "-1-2-84ufpo", out: false),
+        Case(inp: "一些角色", out: false),
+        Case(inp: "九十", out: false),
+        Case(inp: "девяносто", out: false),
+        Case(inp: "09765678987656789876545678987656789876545678", out: true),
+        Case(inp: null, out: false),
       ];
       cases.forEach((c) {
         test("${c.inp} returns ${c.out}", () {
@@ -29,20 +30,20 @@ void main() {
 
     group("#convertYearTo4Digits", () {
       final cases = [
-        _Case(inp: 10, out: 2010),
-        _Case(inp: 100, out: 100),
-        _Case(inp: 1000, out: 1000),
-        _Case(inp: 20, out: 2020),
-        _Case(inp: 2000, out: 2000),
-        _Case(inp: 94, out: 2094),
-        _Case(inp: 2020, out: 2020),
-        _Case(inp: 87656776, out: 87656776),
-        _Case(inp: 8, out: 2008),
-        _Case(inp: 0, out: 2000),
-        _Case(inp: -10, out: -10),
-        _Case(inp: -0, out: 2000),
-        _Case(inp: -88, out: -88),
-        _Case(inp: null, out: 0),
+        Case(inp: 10, out: 2010),
+        Case(inp: 100, out: 100),
+        Case(inp: 1000, out: 1000),
+        Case(inp: 20, out: 2020),
+        Case(inp: 2000, out: 2000),
+        Case(inp: 94, out: 2094),
+        Case(inp: 2020, out: 2020),
+        Case(inp: 87656776, out: 87656776),
+        Case(inp: 8, out: 2008),
+        Case(inp: 0, out: 2000),
+        Case(inp: -10, out: -10),
+        Case(inp: -0, out: 2000),
+        Case(inp: -88, out: -88),
+        Case(inp: null, out: 0),
       ];
       cases.forEach((c) {
         test("${c.inp} returns ${c.out}", () {
@@ -54,20 +55,20 @@ void main() {
 
     group("#hasYearPassed", () {
       final cases = [
-        _Case(inp: 10, out: true),
-        _Case(inp: 100, out: true),
-        _Case(inp: 1000, out: true),
-        _Case(inp: 20, out: false),
-        _Case(inp: 2000, out: true),
-        _Case(inp: 94, out: false),
-        _Case(inp: 2020, out: false),
-        _Case(inp: 87656776, out: false),
-        _Case(inp: 8, out: true),
-        _Case(inp: 0, out: true),
-        _Case(inp: -10, out: true),
-        _Case(inp: -0, out: true),
-        _Case(inp: -88, out: true),
-        _Case(inp: null, out: true),
+        Case(inp: 10, out: true),
+        Case(inp: 100, out: true),
+        Case(inp: 1000, out: true),
+        Case(inp: 20, out: false),
+        Case(inp: 2000, out: true),
+        Case(inp: 94, out: false),
+        Case(inp: 2020, out: false),
+        Case(inp: 87656776, out: false),
+        Case(inp: 8, out: true),
+        Case(inp: 0, out: true),
+        Case(inp: -10, out: true),
+        Case(inp: -0, out: true),
+        Case(inp: -88, out: true),
+        Case(inp: null, out: true),
       ];
       cases.forEach((c) {
         test("${c.inp} returns ${c.out}", () {
@@ -79,17 +80,17 @@ void main() {
 
     group("#hasMonthPassed", () {
       final cases = [
-        _Case(inp: [2020, 10], out: false),
-        _Case(inp: [10, 0], out: true),
-        _Case(inp: [0, 0], out: true),
-        _Case(inp: [1994, 1], out: true),
-        _Case(inp: [1, 1], out: true),
-        _Case(inp: [-203, -13], out: true),
-        _Case(inp: [22, 10], out: false),
-        _Case(inp: [2020, 05], out: false),
-        _Case(inp: [null, 05], out: true),
-        _Case(inp: [24, null], out: true),
-        _Case(inp: [null, null], out: true),
+        Case(inp: [2020, 10], out: false),
+        Case(inp: [10, 0], out: true),
+        Case(inp: [0, 0], out: true),
+        Case(inp: [1994, 1], out: true),
+        Case(inp: [1, 1], out: true),
+        Case(inp: [-203, -13], out: true),
+        Case(inp: [22, 10], out: false),
+        Case(inp: [2020, 05], out: false),
+        Case(inp: [null, 05], out: true),
+        Case(inp: [24, null], out: true),
+        Case(inp: [null, null], out: true),
       ];
       cases.forEach((c) {
         test("${c.inp} returns ${c.out}", () {
@@ -101,14 +102,14 @@ void main() {
 
     group("#isValidMonth", () {
       final cases = [
-        _Case(inp: 10, out: true),
-        _Case(inp: 0, out: false),
-        _Case(inp: -2, out: false),
-        _Case(inp: 1, out: true),
-        _Case(inp: 193873, out: false),
-        _Case(inp: 8, out: true),
-        _Case(inp: 012, out: true),
-        _Case(inp: null, out: false),
+        Case(inp: 10, out: true),
+        Case(inp: 0, out: false),
+        Case(inp: -2, out: false),
+        Case(inp: 1, out: true),
+        Case(inp: 193873, out: false),
+        Case(inp: 8, out: true),
+        Case(inp: 012, out: true),
+        Case(inp: null, out: false),
       ];
       cases.forEach((c) {
         test("${c.inp} returns ${c.out}", () {
@@ -120,16 +121,16 @@ void main() {
 
     group("#isNotExpired", () {
       final cases = [
-        _Case(inp: [2020, 10], out: true),
-        _Case(inp: [10, 0], out: false),
-        _Case(inp: [0, 0], out: false),
-        _Case(inp: [1994, 1], out: false),
-        _Case(inp: [1, 1], out: false),
-        _Case(inp: [-203, -13], out: false),
-        _Case(inp: [22, 10], out: true),
-        _Case(inp: [2020, 05], out: true),
-        _Case(inp: [24, null], out: false),
-        _Case(inp: [null, null], out: false),
+        Case(inp: [2020, 10], out: true),
+        Case(inp: [10, 0], out: false),
+        Case(inp: [0, 0], out: false),
+        Case(inp: [1994, 1], out: false),
+        Case(inp: [1, 1], out: false),
+        Case(inp: [-203, -13], out: false),
+        Case(inp: [22, 10], out: true),
+        Case(inp: [2020, 05], out: true),
+        Case(inp: [24, null], out: false),
+        Case(inp: [null, null], out: false),
       ];
       cases.forEach((c) {
         test("${c.inp} returns ${c.out}", () {
@@ -141,13 +142,13 @@ void main() {
 
     group("#getCleanedNumber", () {
       final cases = [
-        _Case(inp: "poiuytdfghjkkjhb", out: ""),
-        _Case(inp: "098765tgb098eyr", out: "098765098"),
-        _Case(inp: "6d8ge8gf7tfhd=-82qgjs9fh7w6ehf8", out: "6887829768"),
-        _Case(inp: "0", out: "0"),
-        _Case(inp: "девяносто", out: ""),
-        _Case(inp: "一些角色", out: ""),
-        _Case(inp: null, out: ""),
+        Case(inp: "poiuytdfghjkkjhb", out: ""),
+        Case(inp: "098765tgb098eyr", out: "098765098"),
+        Case(inp: "6d8ge8gf7tfhd=-82qgjs9fh7w6ehf8", out: "6887829768"),
+        Case(inp: "0", out: "0"),
+        Case(inp: "девяносто", out: ""),
+        Case(inp: "一些角色", out: ""),
+        Case(inp: null, out: ""),
       ];
 
       cases.forEach((c) {
@@ -160,40 +161,40 @@ void main() {
 
     group("#concatenateCardFields", () {
       final cases = [
-        _Case(
+        Case(
             inp: PaymentCard(
                 number: null, cvc: null, expiryMonth: null, expiryYear: null),
             out: throwsA(TypeMatcher<CardException>())),
-        _Case(inp: null, out: throwsA(TypeMatcher<CardException>())),
-        _Case(
+        Case(inp: null, out: throwsA(TypeMatcher<CardException>())),
+        Case(
             inp: PaymentCard(
                 number: "4111111111111111",
                 cvc: "123",
                 expiryMonth: 12,
                 expiryYear: 12),
             out: "4111111111111111*123*12*12"),
-        _Case(
+        Case(
             inp: PaymentCard(
                 number: "5500000000000004",
                 cvc: null,
                 expiryMonth: 12,
                 expiryYear: 12),
             out: "5500000000000004*null*12*12"),
-        _Case(
+        Case(
             inp: PaymentCard(
                 number: "340000000000009",
                 cvc: "433",
                 expiryMonth: 199,
                 expiryYear: null),
             out: "340000000000009*433*199*0"),
-        _Case(
+        Case(
             inp: PaymentCard(
                 number: "340000000000009",
                 cvc: "433",
                 expiryMonth: null,
                 expiryYear: 30),
             out: "340000000000009*433*0*30"),
-        _Case(
+        Case(
             inp: PaymentCard(
                 number: "340000000000009",
                 cvc: "433",
@@ -217,19 +218,19 @@ void main() {
 
     group("#getExpiryDate", () {
       final cases = [
-        _Case(inp: "poiuytdfghjkkjhb", out: [-1, -1]),
-        _Case(inp: "0/12", out: [0, 12]),
-        _Case(inp: "13/0", out: [13, 0]),
-        _Case(inp: "девяносто/носто", out: [-1, -1]),
-        _Case(inp: "一些角色/12", out: [-1, 12]),
-        _Case(inp: null, out: [-1, -1]),
-        _Case(inp: "12/23", out: [12, 23]),
-        _Case(inp: "-12/-23", out: [-12, -23]),
-        _Case(inp: "13/", out: [13, -1]),
-        _Case(inp: "/", out: [-1, -1]),
-        _Case(inp: "", out: [-1, -1]),
-        _Case(inp: "12/23/14", out: [12, 14]),
-        _Case(inp: "1223", out: [1223, -1]),
+        Case(inp: "poiuytdfghjkkjhb", out: [-1, -1]),
+        Case(inp: "0/12", out: [0, 12]),
+        Case(inp: "13/0", out: [13, 0]),
+        Case(inp: "девяносто/носто", out: [-1, -1]),
+        Case(inp: "一些角色/12", out: [-1, 12]),
+        Case(inp: null, out: [-1, -1]),
+        Case(inp: "12/23", out: [12, 23]),
+        Case(inp: "-12/-23", out: [-12, -23]),
+        Case(inp: "13/", out: [13, -1]),
+        Case(inp: "/", out: [-1, -1]),
+        Case(inp: "", out: [-1, -1]),
+        Case(inp: "12/23/14", out: [12, 14]),
+        Case(inp: "1223", out: [1223, -1]),
       ];
 
       cases.forEach((c) {
@@ -241,10 +242,3 @@ void main() {
     });
   });
 }
-
-class _Case {
-  dynamic inp;
-  dynamic out;
-
-  _Case({@required this.inp, @required this.out});
-}
diff --git a/test/src/common/case.dart b/test/src/common/case.dart
new file mode 100644
index 00000000..fec53294
--- /dev/null
+++ b/test/src/common/case.dart
@@ -0,0 +1,8 @@
+import 'package:meta/meta.dart';
+
+class Case {
+  dynamic inp;
+  dynamic out;
+
+  Case({@required this.inp, @required this.out});
+}
diff --git a/test/src/common/string_utils_test.dart b/test/src/common/string_utils_test.dart
new file mode 100644
index 00000000..4c70bbfe
--- /dev/null
+++ b/test/src/common/string_utils_test.dart
@@ -0,0 +1,66 @@
+import 'package:flutter_paystack/src/common/string_utils.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'case.dart';
+
+void main() {
+  group("$StringUtils", () {
+    group("#isEmpty", () {
+      final cases = [
+        Case(inp: "876jje", out: false),
+        Case(inp: "@", out: false),
+        Case(inp: "12344323", out: false),
+        Case(inp: "null", out: true),
+        Case(inp: null, out: true),
+        Case(inp: "娱乐", out: false),
+        Case(inp: "развлекательная", out: false),
+      ];
+      cases.forEach((c) {
+        test("${c.inp} returns ${c.out}", () {
+          final value = StringUtils.isEmpty(c.inp);
+          expect(c.out, value);
+        });
+      });
+    });
+
+    group("#isValidEmail", () {
+      final cases = [
+        Case(inp: "email", out: false),
+        Case(inp: "@", out: false),
+        Case(inp: ".com", out: false),
+        Case(inp: "email@.com", out: false),
+        Case(inp: "email@host.com", out: true),
+        Case(inp: "ema-il@host-h.com", out: true),
+        Case(inp: "e_mail@host-j.gov", out: true),
+        Case(inp: "asdf@adsf.adsf", out: true),
+        Case(inp: "развлекательная@adsf.adsf", out: false),
+        Case(inp: "1234444", out: false),
+        Case(inp: "null", out: false),
+        Case(inp: null, out: false),
+      ];
+      cases.forEach((c) {
+        test("${c.inp} returns ${c.out}", () {
+          final value = StringUtils.isValidEmail(c.inp);
+          expect(c.out, value);
+        });
+      });
+    });
+
+    group("#nullify", () {
+      final cases = [
+        Case(inp: "you", out: "you"),
+        Case(inp: "развлекательная", out: "развлекательная"),
+        Case(inp: "娱乐", out: "娱乐"),
+        Case(inp: "", out: null),
+        Case(inp: '', out: null),
+        Case(inp: null, out: isNot(equals("q"))),
+      ];
+      cases.forEach((c) {
+        test("${c.inp} returns ${c.out}", () {
+          final value = StringUtils.nullify(c.inp);
+          expect(value, c.out);
+        });
+      });
+    });
+  });
+}
diff --git a/test/src/common/utils_test.dart b/test/src/common/utils_test.dart
new file mode 100644
index 00000000..b23d9cce
--- /dev/null
+++ b/test/src/common/utils_test.dart
@@ -0,0 +1,174 @@
+import 'dart:io';
+
+import 'package:flutter/services.dart';
+import 'package:flutter_paystack/flutter_paystack.dart';
+import 'package:flutter_paystack/src/common/my_strings.dart';
+import 'package:flutter_paystack/src/common/utils.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:matcher/matcher.dart';
+
+void main() {
+  const MethodChannel channel = MethodChannel('flutter_paystack');
+
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  setUp(() {
+    channel.setMockMethodCallHandler((MethodCall methodCall) async {
+      return '';
+    });
+  });
+
+  tearDown(() {
+    channel.setMockMethodCallHandler(null);
+  });
+
+  group("$Utils", () {
+    group("#validateSdkInitialized", () {
+      test(
+          "throws PaystackSdkNotInitializedException when PaystackPlugin is not initialized",
+          () {
+        expect(() => Utils.validateSdkInitialized(),
+            throwsA(TypeMatcher<PaystackSdkNotInitializedException>()));
+      });
+
+      test("returns normally when PaystackPlugin is initialized", () async {
+        await PaystackPlugin.initialize(
+            publicKey: Platform.environment["PAYSTACK_TEST_PUBLIC_KEY"]);
+        expect(() => Utils.validateSdkInitialized(), returnsNormally);
+        PaystackPlugin.dispose();
+      });
+    });
+
+    group("#getKeyErrorMsg", () {
+      test("returns a string with keyType", () {
+        final keyType = "public";
+        expect(Utils.getKeyErrorMsg(keyType), contains(keyType));
+      });
+    });
+
+    group("#formatAmount", () {
+      test("throws Error when currency formatter is not set", () {
+        expect(() => Utils.formatAmount(100), throwsA(TypeMatcher<String>()));
+      });
+
+      test("returns normally when currency formatter has been set", () {
+        Utils.setCurrencyFormatter(Strings.ngn, Strings.nigerianLocale);
+        expect(() => Utils.formatAmount(100), returnsNormally);
+      });
+    });
+
+    group("#validateChargeAndKey", () {
+      test(
+          "throws PaystackSdkNotInitializedException when called with null charge and PaystackPlugin is not initialized",
+          () {
+        expect(() => Utils.validateChargeAndKey(null),
+            throwsA(TypeMatcher<PaystackSdkNotInitializedException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws PaystackSdkNotInitializedException when called with charge and PaystackPlugin is not initialized",
+          () {
+        expect(() {
+          var charge = Charge()
+            ..email = "email@e.co"
+            ..amount = 100;
+          return Utils.validateChargeAndKey(charge);
+        }, throwsA(TypeMatcher<PaystackSdkNotInitializedException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws AuthenticationException when called with null charge and PaystackPlugin is initialized with invalid key",
+          () async {
+        await PaystackPlugin.initialize(publicKey: "ytryuiuyuiuyfg");
+        expect(() => Utils.validateChargeAndKey(null),
+            throwsA(TypeMatcher<AuthenticationException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws AuthenticationException when called with charge and PaystackPlugin is initialized with invalid key",
+          () async {
+        await PaystackPlugin.initialize(publicKey: "ytryuiuyuiuyfg");
+        var charge = Charge()
+          ..email = "email@e.co"
+          ..amount = 100;
+        expect(() => Utils.validateChargeAndKey(charge),
+            throwsA(TypeMatcher<AuthenticationException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws PaystackException when called with null charge and PaystackPlugin is initialized with valid key",
+          () async {
+        await PaystackPlugin.initialize(
+            publicKey: Platform.environment["PAYSTACK_TEST_PUBLIC_KEY"]);
+        expect(() => Utils.validateChargeAndKey(null),
+            throwsA(TypeMatcher<PaystackException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws InvalidAmountException when called with null amount and PaystackPlugin is initialized with valid key",
+          () async {
+        await PaystackPlugin.initialize(
+            publicKey: Platform.environment["PAYSTACK_TEST_PUBLIC_KEY"]);
+        expect(() => Utils.validateChargeAndKey(Charge()..email = "you@u.com"),
+            throwsA(TypeMatcher<InvalidAmountException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws InvalidAmountException when called with negative amount and PaystackPlugin is initialized with valid key",
+          () async {
+        await PaystackPlugin.initialize(
+            publicKey: Platform.environment["PAYSTACK_TEST_PUBLIC_KEY"]);
+        expect(() {
+          var charge = Charge()
+            ..email = "you@u.com"
+            ..amount = -10;
+          return Utils.validateChargeAndKey(charge);
+        }, throwsA(TypeMatcher<InvalidAmountException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws InvalidAmountException when called with valid amount, null email and PaystackPlugin is initialized with valid key",
+          () async {
+        await PaystackPlugin.initialize(
+            publicKey: Platform.environment["PAYSTACK_TEST_PUBLIC_KEY"]);
+        expect(() {
+          var charge = Charge()..amount = 10;
+          return Utils.validateChargeAndKey(charge);
+        }, throwsA(TypeMatcher<InvalidEmailException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "throws InvalidAmountException when called with valid amount, invalid email and PaystackPlugin is initialized with valid key",
+          () async {
+        await PaystackPlugin.initialize(
+            publicKey: Platform.environment["PAYSTACK_TEST_PUBLIC_KEY"]);
+        var charge = Charge()
+          ..amount = 10
+          ..email = "8yu";
+        expect(() => Utils.validateChargeAndKey(charge),
+            throwsA(TypeMatcher<InvalidEmailException>()));
+        PaystackPlugin.dispose();
+      });
+
+      test(
+          "returns normally when called with valid charge and PaystackPlugin is initialized with valid key",
+          () async {
+        await PaystackPlugin.initialize(
+            publicKey: Platform.environment["PAYSTACK_TEST_PUBLIC_KEY"]);
+        var charge = Charge()
+          ..amount = 10
+          ..email = "8yu@h.go";
+        expect(() => Utils.validateChargeAndKey(charge), returnsNormally);
+        PaystackPlugin.dispose();
+      });
+    });
+  });
+}