diff --git a/.circleci/config.yml b/.circleci/config.yml
deleted file mode 100644
index edbcd3d..0000000
--- a/.circleci/config.yml
+++ /dev/null
@@ -1,30 +0,0 @@
-version: 2.1
-jobs:
-  build:
-    docker:
-      - image: circleci/ruby:2.6.1
-        environment:
-          RAILS_ENV: test
-    steps:
-      - checkout
-      - run:
-          name: Which bundler?
-          command: bundle -v
-
-      - restore_cache:
-          keys:
-            - zilliqa{{ checksum "Gemfile.lock" }}
-            - zilliqa
-
-      - run:
-          name: Install libsecp256k1-dev dependency
-          command: sudo apt-get update -y && sudo apt-get install -y libsecp256k1-dev
-
-      - run:
-          name: Bundle Install
-          command: bundle install
-      - save_cache:
-          key: zilliqa{{ checksum "Gemfile.lock" }}
-          paths:
-            - vendor/bundle
-      - run: bundle exec rake test
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..128bc32
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,27 @@
+name: CI
+
+on:
+  pull_request:
+    types: [opened, labeled, reopened, synchronize]
+  push:
+    branches: [master]
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    name: test
+    steps:
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.7.3
+          rubygems: latest
+          bundler-cache: true
+      - uses: actions/checkout@v3
+      - run: sudo apt-get update -y && sudo apt-get install -y libsecp256k1-dev
+      - run: bundle install
+      - run: bundle exec rake test
diff --git a/Gemfile.lock b/Gemfile.lock
index 6f237c4..1b1cad5 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -17,6 +17,8 @@ GEM
       eventmachine
       ffi
       scrypt
+    byebug (11.1.3)
+    coderay (1.1.3)
     eventmachine (1.2.7)
     faraday (2.7.10)
       faraday-net_http (>= 2.0, < 3.1)
@@ -30,9 +32,16 @@ GEM
     jsonrpc-client (0.1.4)
       faraday
       multi_json (>= 1.1.0)
-    minitest (5.16.1)
+    method_source (1.0.0)
+    minitest (5.15.0)
     multi_json (1.15.0)
     pbkdf2-ruby (0.2.1)
+    pry (0.14.2)
+      coderay (~> 1.1)
+      method_source (~> 1.0)
+    pry-byebug (3.10.1)
+      byebug (~> 11.0)
+      pry (>= 0.13, < 0.15)
     rake (13.0.6)
     ruby-bitcoin-secp256k1 (0.5.2)
       ffi (>= 1.9.25)
@@ -44,7 +53,8 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  minitest (~> 5.0)
+  minitest (= 5.15)
+  pry-byebug (~> 3.10)
   rake (~> 13.0)
   zilliqa!
 
diff --git a/lib/zilliqa/util/validator.rb b/lib/zilliqa/util/validator.rb
index 92a4037..3875f42 100644
--- a/lib/zilliqa/util/validator.rb
+++ b/lib/zilliqa/util/validator.rb
@@ -22,16 +22,6 @@ def self.signature?(signature)
         m != nil
       end
 
-      # checksum_address?
-      #
-      # takes hex-encoded string and returns boolean if address is checksumed
-      #
-      # @param {string} address
-      # @returns {boolean}
-      def self.checksum_address?(address)
-        self.address?(address) && Zilliqa::Account::Wallet::to_checksum_address(address) == address
-      end
-
       def self.bech32?(address)
         m = /^zil1[qpzry9x8gf2tvdw0s3jn54khce6mua7l]{38}/ =~ address
         m != nil
diff --git a/test/account/transaction_test.rb b/test/account/transaction_test.rb
index 798c64f..553ebac 100644
--- a/test/account/transaction_test.rb
+++ b/test/account/transaction_test.rb
@@ -12,19 +12,6 @@ def setup
     end
   end
 
-  def test_return_a_checksummed_address_from_tx_params
-    tx_params = {
-      version: 0,
-      amount: '0',
-      gas_price: '1000',
-      gas_limit: 1000,
-      to_addr: '2E3C9B415B19AE4035503A06192A0FAD76E04243'
-    }
-
-    tx = Zilliqa::Account::Transaction.new(tx_params, nil)
-    assert Zilliqa::Util::Validator.checksum_address?(tx.to_payload[:toAddr])
-  end
-
   def test_should_poll_and_call_queued_handlers_on_confirmation
     responses = [
       {
@@ -66,7 +53,6 @@ def test_should_poll_and_call_queued_handlers_on_confirmation
     tx = Zilliqa::Account::Transaction.new(tx_params, @provider)
 
     @provider.expect("GetBalance", responses[0], [@address])
-    @provider.expect("testnet?", false)
     pending = @wallet.sign(tx)
 
     @provider.expect("GetTransaction", responses[2], ['some_hash'])
@@ -229,15 +215,14 @@ def test_encode_transaction_proto_for_null_code_and_null_data
   def test_devnet
     id = nil
     version = 21_823_489
-    gas_price = '1000000000'
-    gas_limit = 1
+    gas_price = '2000000000'
+    gas_limit = 50
 
     sender_pub_key = '027eaa76955940798e22ec4007b00dbf0002fcd34f501f58c04b06c604f2228076'
     to_addr = '0xFeEd7997A0a45682CD4D8CEda27f2d81F6ba587c'
     amount = '1000000000000'
 
     provider = Zilliqa::Jsonrpc::Provider.new('https://dev-api.zilliqa.com')
-    @provider.expect("testnet?", true)
     signer = Zilliqa::Account::Wallet.new(provider)
 
     private_key = '7e78c742bca06824e4a5f0591260a2646339507c231daa5a47bf91d801f98239'
@@ -259,7 +244,6 @@ def test_devnet
 
     signed = signer.sign(tx)
     payload = signed.to_payload
-    puts payload
 
     provider.CreateTransaction(payload)
   end
diff --git a/test/account/wallet_test.rb b/test/account/wallet_test.rb
index ca8638d..97b61d9 100644
--- a/test/account/wallet_test.rb
+++ b/test/account/wallet_test.rb
@@ -1,19 +1,6 @@
 require 'test_helper'
 
 class WalletTest < Minitest::Test
-  def test_to_checksum_address
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('4BAF5FADA8E5DB92C3D3242618C5B47133AE003C'), '0x4BAF5faDA8e5Db92C3d3242618c5B47133AE003C'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('448261915A80CDE9BDE7C7A791685200D3A0BF4E'), '0x448261915a80cdE9BDE7C7a791685200D3A0bf4E'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('DED02FD979FC2E55C0243BD2F52DF022C40ADA1E'), '0xDed02fD979fC2e55c0243bd2F52df022c40ADa1E'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('13F06E60297BEA6A3C402F6F64C416A6B31E586E'), '0x13F06E60297bea6A3c402F6f64c416A6b31e586e'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('1A90C25307C3CC71958A83FA213A2362D859CF33'), '0x1a90C25307C3Cc71958A83fa213A2362D859CF33'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('625ABAEBD87DAE9AB128F3B3AE99688813D9C5DF'), '0x625ABAebd87daE9ab128f3B3AE99688813d9C5dF'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('36BA34097F861191C48C839C9B1A8B5912F583CF'), '0x36Ba34097f861191C48C839c9b1a8B5912f583cF'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('D2453AE76C9A86AAE544FCA699DBDC5C576AEF3A'), '0xD2453Ae76C9A86AAe544fca699DbDC5c576aEf3A'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('72220E84947C36118CDBC580454DFAA3B918CD97'), '0x72220e84947c36118cDbC580454DFaa3b918cD97'
-    assert_equal Zilliqa::Account::Wallet.to_checksum_address('50F92304C892D94A385CA6CE6CD6950CE9A36839'), '0x50f92304c892D94A385cA6cE6CD6950ce9A36839'
-  end
-
   def test_create
     wallet = Zilliqa::Account::Wallet.new(nil, {})
     address = wallet.create
@@ -42,7 +29,6 @@ def test_sign
 
     provider = Minitest::Mock.new
     wallet = Zilliqa::Account::Wallet.new(provider, {})
-    provider.expect("testnet?", false)
     wallet.add_by_private_key(private_key)
 
     tx_params = {
@@ -90,11 +76,9 @@ def test_invalid_signature
     account = Zilliqa::Account::Account.new(private_key)
     wallet.add_by_private_key(private_key)
 
-    provider.expect('testnet?', false)
     provider.expect('GetBalance', response, [address])
 
     100.times do |i|
-      provider.expect('testnet?', false)
       provider.expect('GetBalance', response, [address])
 
       tx_params = {
diff --git a/test/contract/contract_factory_test.rb b/test/contract/contract_factory_test.rb
index fb5ada2..b68cdcf 100644
--- a/test/contract/contract_factory_test.rb
+++ b/test/contract/contract_factory_test.rb
@@ -85,7 +85,6 @@ def test_should_be_able_to_deploy_a_contract
     @provider.expect("GetBalance", responses[0], [@address])
     @provider.expect("CreateTransaction", responses[1], [Hash])
     @provider.expect("GetTransaction", responses[2], ['some_hash'])
-    @provider.expect("testnet?", false)
 
     deploy_params = Zilliqa::Contract::DeployParams.new(nil, Zilliqa::Util.pack(8, 8), nil, 1000, 1000, nil)
     tx, deployed = contract.deploy(deploy_params)
@@ -96,7 +95,7 @@ def test_should_be_able_to_deploy_a_contract
     assert deployed.deployed?
     assert_equal Zilliqa::Contract::ContractStatus::DEPLOYED, deployed.status
 
-    assert /[A-F0-9]+/ =~ contract.address
+    assert(/[A-F0-9]+/ =~ contract.address)
   end
 
   def test_should_not_swallow_network_errors
@@ -135,7 +134,6 @@ def test_should_not_swallow_network_errors
     end
 
     @provider.expect("GetBalance", responses[0], [@address])
-    @provider.expect("testnet?", false)
 
     def @provider.CreateTransaction(payload)
       raise 'something bad happened'
@@ -143,7 +141,7 @@ def @provider.CreateTransaction(payload)
 
     deploy_params = Zilliqa::Contract::DeployParams.new(nil, Zilliqa::Util.pack(8, 8), nil, 1000, 1000, nil)
     assert_raises 'something bad happened.' do
-      tx, deployed = contract.deploy(deploy_params)
+      contract.deploy(deploy_params)
     end
 
     @provider.verify
@@ -186,7 +184,6 @@ def test_if_the_underlying_transaction_is_rejected_contract_status_should_be_rej
 
     @provider.expect("GetBalance", responses[0], [@address])
     @provider.expect("CreateTransaction", responses[1], [Hash])
-    @provider.expect("testnet?", false)
 
     deploy_params = Zilliqa::Contract::DeployParams.new(nil, Zilliqa::Util.pack(8, 8), nil, 1000, 1000, nil)
     tx, contract = contract.deploy(deploy_params)
@@ -246,7 +243,6 @@ def test_if_the_transaction_receipt_success_equal_false_contract_status_should_b
     @provider.expect("GetBalance", responses[0], [@address])
     @provider.expect("CreateTransaction", responses[1], [Hash])
     @provider.expect("GetTransaction", responses[2], ['some_hash'])
-    @provider.expect("testnet?", false)
 
     deploy_params = Zilliqa::Contract::DeployParams.new(nil, Zilliqa::Util.pack(8, 8), nil, 1000, 1000, nil)
     tx, contract = contract.deploy(deploy_params)
@@ -329,17 +325,15 @@ def test_should_be_able_to_call_a_transition
       JSON.parse(JSON.generate(res))
     end
 
-    @provider.expect("testnet?", false)
     @provider.expect("GetBalance", responses[0], [@address])
     @provider.expect("CreateTransaction", responses[1], [Hash])
     @provider.expect("GetTransaction", responses[2], ['some_hash'])
     @provider.expect("GetBalance", responses[3], [@address])
     @provider.expect("CreateTransaction", responses[4], [Hash])
     @provider.expect("GetTransaction", responses[5], ['some_hash'])
-    @provider.expect("testnet?", false)
 
     deploy_params = Zilliqa::Contract::DeployParams.new(nil, Zilliqa::Util.pack(8, 8), nil, 1000, 1000, nil)
-    tx, contract = contract.deploy(deploy_params)
+    _, contract = contract.deploy(deploy_params)
 
     call_tx = contract.call(
       'myTransition',
diff --git a/test/test_helper.rb b/test/test_helper.rb
index d786b29..8802967 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -2,3 +2,4 @@
 require "zilliqa"
 
 require "minitest/autorun"
+require "pry-byebug"
diff --git a/test/util/validator_test.rb b/test/util/validator_test.rb
index 9d1b456..0783291 100644
--- a/test/util/validator_test.rb
+++ b/test/util/validator_test.rb
@@ -30,13 +30,6 @@ def test_address?
     assert Zilliqa::Util::Validator.address?(address)
   end
 
-  def test_checksum_address?
-    checksum_address = '0x4BAF5faDA8e5Db92C3d3242618c5B47133AE003C'
-    assert Zilliqa::Util::Validator.checksum_address?(checksum_address)
-    assert !Zilliqa::Util::Validator.checksum_address?(checksum_address[0..-2])
-    assert !Zilliqa::Util::Validator.checksum_address?(checksum_address.upcase)
-  end
-
   def test_bech32?
     address = 'zil1ej8wy3mnux6t9zeuc4vkhww0csctfpznzt4s76'
 
diff --git a/zilliqa.gemspec b/zilliqa.gemspec
index d1fa937..bbf89dc 100644
--- a/zilliqa.gemspec
+++ b/zilliqa.gemspec
@@ -36,7 +36,11 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency "bundler", ">= 2.2.33"
   spec.add_development_dependency "rake", "~> 13.0"
-  spec.add_development_dependency "minitest", "~> 5.0"
+  # FIXME starting with 5.16 minitest supports kwargs in mocks,
+  # and that breaks our tests, e.g in contract/contract_factory_test.rb:186,
+  # where we expect hash as mock argument, but minitest treat this hash as kwargs
+  spec.add_development_dependency "minitest", "5.15"
+  spec.add_development_dependency "pry-byebug", "~> 3.10"
   spec.add_dependency "ruby-bitcoin-secp256k1"
   spec.add_dependency "scrypt"
   spec.add_dependency "pbkdf2-ruby"