diff --git a/test/support/test_token.ex b/test/support/test_token.ex
index 7b11b63..0ff0051 100644
--- a/test/support/test_token.ex
+++ b/test/support/test_token.ex
@@ -1,4 +1,5 @@
 defmodule TTEth.TestToken do
+  @moduledoc false
   use TTEth.Contract,
     abi_file: Application.app_dir(:tt_eth, "priv/fixtures/contract_abis/TestToken.abi")
 end
diff --git a/test/tt_eth/transactions/eip1559_transaction_test.exs b/test/tt_eth/transactions/eip1559_transaction_test.exs
index 1597a62..a19aad8 100644
--- a/test/tt_eth/transactions/eip1559_transaction_test.exs
+++ b/test/tt_eth/transactions/eip1559_transaction_test.exs
@@ -5,7 +5,7 @@ defmodule TTEth.Transactions.EIP1559TransactionTest do
   alias TTEth.Wallet
 
   # Polygon Mumbai.
-  @chain_id 80001
+  @chain_id 80_001
 
   @private_key_human "0x62aa6ec41b56439d2c5df352c45a00389cef262b3761e13c6481e35ab027d262"
   @to_address_human "0x38f153fdd399ff2cf64704c6a4b16d3fd9ddcd69"
@@ -113,7 +113,7 @@ defmodule TTEth.Transactions.EIP1559TransactionTest do
         data: @tx_data,
         chain_id: @chain_id,
         nonce: @nonce,
-        gas_limit: 21000,
+        gas_limit: 21_000,
         max_fee_per_gas: 3_000_000_000,
         max_priority_fee_per_gas: 3_000_000_001,
         value: 0
diff --git a/test/tt_eth/wallet_test.exs b/test/tt_eth/wallet_test.exs
index f56b324..24b3e41 100644
--- a/test/tt_eth/wallet_test.exs
+++ b/test/tt_eth/wallet_test.exs
@@ -39,6 +39,64 @@ defmodule TTEth.WalletTest do
     end
   end
 
+  describe "sign/2" do
+    setup :build_wallet
+
+    test "given a wallet and digest, signs the digest", %{wallet: wallet} do
+      wallet
+      |> Wallet.sign("some plaintext" |> TTEth.keccak())
+      |> assert_match({:ok, {<<_signature::512>>, recovery_id}} when recovery_id in [0, 1])
+    end
+
+    test "returns an error tuple if a failure happens", %{wallet: wallet} do
+      wallet
+      |> Wallet.sign("some plaintext")
+      |> assert_equal({:error, :wrong_message_size})
+    end
+  end
+
+  describe "sign!/2" do
+    setup :build_wallet
+
+    test "same as sign/2", %{wallet: wallet} do
+      digest = "some plaintext" |> TTEth.keccak()
+
+      {:ok, compact_signature} =
+        wallet
+        |> Wallet.sign(digest)
+
+      wallet
+      |> Wallet.sign!(digest)
+      |> assert_match(^compact_signature)
+    end
+  end
+
+  describe "personal_sign/2" do
+    setup :build_wallet
+
+    test "signs a plaintext using the EIP-191 standard", %{wallet: wallet} do
+      wallet
+      |> Wallet.personal_sign("some plaintext")
+      |> assert_match({:ok, {v, _r, _s}} when v in [27, 28])
+    end
+
+    test "returns an error tuple if a failure happens"
+  end
+
+  describe "personal_sign!/2" do
+    setup :build_wallet
+
+    test "same as personal_sign/2", %{wallet: wallet} do
+      {:ok, components} =
+        wallet
+        |> Wallet.personal_sign("some plaintext")
+
+      wallet
+      |> Wallet.personal_sign!("some plaintext")
+      |> assert_match(^components)
+    end
+  end
+
   ## Private.
 
   defp assert_match_ternary_wallet(wallet) do
@@ -65,4 +123,7 @@ defmodule TTEth.WalletTest do
       }
     })
   end
+
+  defp build_wallet(_),
+    do: %{wallet: Wallet.new()}
 end
diff --git a/test/tt_eth_test.exs b/test/tt_eth_test.exs
index 06c4f0c..1971076 100644
--- a/test/tt_eth_test.exs
+++ b/test/tt_eth_test.exs
@@ -3,7 +3,7 @@ defmodule TTEthTest do
   import TTEth, only: [binary_to_hex!: 1]
   doctest TTEth, import: true
 
-  @chain_id 12345
+  @chain_id 12_345
 
   describe "new_keypair/0" do
     test "generates a public and private key" do