diff --git a/Cargo.toml b/Cargo.toml
index 7b7c523..6652d97 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,14 +10,17 @@ license = "MIT OR Apache-2.0"
 readme = "README.md"
 edition = "2018"
 
+[features]
+no-chip-version-assertion = []
+
 [dependencies]
 byteorder = { version = "1.3.4", default-features = false }
-embedded-hal = "0.2.4"
+embedded-hal = "0.2"
 embedded-nal = "0.6.0"
-bit_field = "0.10.1"
+bit_field = "0.10"
 derive-try-from-primitive = "1"
 nb = "1.0.0"
 defmt = { version = "0.3", optional = true }
 
-[features]
-no-chip-version-assertion = []
+[dev-dependencies]
+embedded-hal-mock = "0.9"
\ No newline at end of file
diff --git a/src/bus/four_wire.rs b/src/bus/four_wire.rs
index f33f5d5..4640191 100644
--- a/src/bus/four_wire.rs
+++ b/src/bus/four_wire.rs
@@ -29,10 +29,13 @@ impl<Spi: Transfer<u8> + Write<u8>, ChipSelect: OutputPin> FourWire<Spi, ChipSel
 impl<Spi: Transfer<u8> + Write<u8>, ChipSelect: OutputPin> Bus for FourWire<Spi, ChipSelect> {
     type Error =
         FourWireError<<Spi as Transfer<u8>>::Error, <Spi as Write<u8>>::Error, ChipSelect::Error>;
+
     fn read_frame(&mut self, block: u8, address: u16, data: &mut [u8]) -> Result<(), Self::Error> {
         let address_phase = address.to_be_bytes();
         let control_phase = block << 3;
         let data_phase = data;
+
+        // set Chip select to Low, i.e. prepare to receive data
         self.cs.set_low().map_err(FourWireError::ChipSelectError)?;
         let result = (|| {
             self.spi
@@ -44,29 +47,39 @@ impl<Spi: Transfer<u8> + Write<u8>, ChipSelect: OutputPin> Bus for FourWire<Spi,
                 .map_err(FourWireError::TransferError)?;
             Ok(())
         })();
+
+        // set Chip select to High, i.e. we've finished listening
         self.cs.set_high().map_err(FourWireError::ChipSelectError)?;
+
+        // then return the result of the transmission
         result
     }
+
     fn write_frame(&mut self, block: u8, address: u16, data: &[u8]) -> Result<(), Self::Error> {
         let address_phase = address.to_be_bytes();
         let control_phase = block << 3 | WRITE_MODE_MASK;
         let data_phase = data;
+
+        // set Chip select to Low, i.e. prepare to transmit
         self.cs.set_low().map_err(FourWireError::ChipSelectError)?;
-        let result = (|| {
-            self.spi
-                .write(&address_phase)
-                .and_then(|_| self.spi.write(&[control_phase]))
-                .and_then(|_| self.spi.write(data_phase))
-                .map_err(FourWireError::WriteError)?;
-            Ok(())
-        })();
+        let result = self
+            .spi
+            .write(&address_phase)
+            .and_then(|_| self.spi.write(&[control_phase]))
+            .and_then(|_| self.spi.write(data_phase))
+            .map_err(FourWireError::WriteError);
+
+        // set Chip select to High, i.e. we've finished transmitting
         self.cs.set_high().map_err(FourWireError::ChipSelectError)?;
+
+        // then return the result of the transmission
         result
     }
 }
 
 // Must use map_err, ambiguity prevents From from being implemented
 #[repr(u8)]
+#[derive(Clone)]
 pub enum FourWireError<TransferError, WriteError, ChipSelectError> {
     TransferError(TransferError),
     WriteError(WriteError),
@@ -91,3 +104,90 @@ impl<TransferError, WriteError, ChipSelectError> fmt::Debug
 
 // TODO Improved error rendering could be done with specialization.
 // https://github.com/rust-lang/rust/issues/31844
+
+#[cfg(test)]
+mod test {
+    use embedded_hal::digital::v2::OutputPin;
+    use embedded_hal_mock::{
+        pin::{Mock as PinMock, State as PinState, Transaction as PinTransaction},
+        spi::{Mock as SpiMock, Transaction as SpiTransaction},
+    };
+
+    use crate::{
+        bus::{four_wire::WRITE_MODE_MASK, Bus},
+        register,
+    };
+
+    use super::FourWire;
+
+    #[test]
+    fn test_read_frame() {
+        let mut cs_pin = PinMock::new(&[
+            // we begin with pin HIGH
+            PinTransaction::set(PinState::High),
+            // When reading
+            PinTransaction::set(PinState::Low),
+            // When finished reading
+            PinTransaction::set(PinState::High),
+        ]);
+
+        // initiate the pin to high.
+        cs_pin.set_high().expect("Should set pin to high");
+
+        let mut actual_version = [0_u8; 1];
+        let mut expected_version = 5;
+
+        let expectations = [
+            SpiTransaction::write(register::common::VERSION.to_be_bytes().to_vec()),
+            SpiTransaction::write(vec![register::COMMON << 3]),
+            SpiTransaction::transfer(actual_version.to_vec(), vec![expected_version]),
+        ];
+
+        let mock_spi = SpiMock::new(&expectations);
+
+        let mut four_wire = FourWire::new(mock_spi, cs_pin);
+
+        four_wire.read_frame(
+            register::COMMON,
+            register::common::VERSION,
+            &mut actual_version,
+        );
+
+        assert_eq!(expected_version, actual_version[0]);
+    }
+
+    #[test]
+    fn test_write_frame() {
+        let mut cs_pin = PinMock::new(&[
+            // we begin with pin HIGH
+            PinTransaction::set(PinState::High),
+            // When reading
+            PinTransaction::set(PinState::Low),
+            // When finished reading
+            PinTransaction::set(PinState::High),
+        ]);
+
+        // initiate the pin to high.
+        cs_pin.set_high().expect("Should set pin to high");
+
+        let socket_0_reg = 0x01_u8;
+        let socket_1_reg = 0x05_u8;
+        let source_port = 49849_u16;
+
+        let expectations = [
+            SpiTransaction::write(register::socketn::SOURCE_PORT.to_be_bytes().to_vec()),
+            SpiTransaction::write(vec![socket_1_reg << 3 | WRITE_MODE_MASK]),
+            SpiTransaction::write(source_port.to_be_bytes().to_vec()),
+        ];
+
+        let mock_spi = SpiMock::new(&expectations);
+
+        let mut four_wire = FourWire::new(mock_spi, cs_pin);
+
+        four_wire.write_frame(
+            socket_1_reg,
+            register::socketn::SOURCE_PORT,
+            &source_port.to_be_bytes(),
+        );
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 475ba9e..9c430ba 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,4 @@
-#![no_std]
+#![cfg_attr(not(test), no_std)]
 #![allow(unused)]
 #![deny(rustdoc::broken_intra_doc_links)]
 #![doc = include_str!("../README.md")]