diff --git a/Cargo.lock b/Cargo.lock
index d3bea91a1f..8b7dd9f744 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -10328,6 +10328,7 @@ dependencies = [
 name = "starknet_l1_provider"
 version = "0.0.0"
 dependencies = [
+ "assert_matches",
  "papyrus_base_layer",
  "starknet_api",
  "thiserror",
diff --git a/crates/starknet_l1_provider/Cargo.toml b/crates/starknet_l1_provider/Cargo.toml
index f9ac23e999..2340234fcb 100644
--- a/crates/starknet_l1_provider/Cargo.toml
+++ b/crates/starknet_l1_provider/Cargo.toml
@@ -10,5 +10,8 @@ papyrus_base_layer.workspace = true
 starknet_api.workspace = true
 thiserror.workspace = true
 
+[dev-dependencies]
+assert_matches.workspace = true
+
 [lints]
 workspace = true
diff --git a/crates/starknet_l1_provider/src/errors.rs b/crates/starknet_l1_provider/src/errors.rs
index 487dc62696..22dc68d22b 100644
--- a/crates/starknet_l1_provider/src/errors.rs
+++ b/crates/starknet_l1_provider/src/errors.rs
@@ -1,6 +1,8 @@
 use papyrus_base_layer::ethereum_base_layer_contract::EthereumBaseLayerError;
 use thiserror::Error;
 
+use crate::ProviderState;
+
 #[derive(Error, Debug)]
 pub enum L1ProviderError {
     #[error(transparent)]
@@ -11,8 +13,8 @@ pub enum L1ProviderError {
     GetTransactionsInPendingState,
     #[error("`get_txs` while in validate state")]
     GetTransactionConsensusBug,
-    #[error("Can not set state: {0}")]
-    UnexpectedState(String),
+    #[error("Cannot transition from {from} to {to}")]
+    UnexpectedProviderStateTransition { from: ProviderState, to: ProviderState },
     #[error("`validate_tx` called while in proposal state")]
     ValidateTransactionConsensusBug,
 }
diff --git a/crates/starknet_l1_provider/src/l1_provider_tests.rs b/crates/starknet_l1_provider/src/l1_provider_tests.rs
new file mode 100644
index 0000000000..be8dcbc608
--- /dev/null
+++ b/crates/starknet_l1_provider/src/l1_provider_tests.rs
@@ -0,0 +1,20 @@
+use assert_matches::assert_matches;
+
+use crate::errors::L1ProviderError::UnexpectedProviderStateTransition;
+use crate::{L1Provider, ProviderState};
+
+#[test]
+fn proposal_start_errors() {
+    // Setup.
+    let mut l1_provider = L1Provider::default();
+
+    // Test.
+    l1_provider.proposal_start().unwrap();
+    assert_matches!(
+        l1_provider.proposal_start().unwrap_err(),
+        UnexpectedProviderStateTransition {
+            from: ProviderState::Propose,
+            to: ProviderState::Propose
+        }
+    );
+}
diff --git a/crates/starknet_l1_provider/src/lib.rs b/crates/starknet_l1_provider/src/lib.rs
index 10fda6bf7c..557402c48e 100644
--- a/crates/starknet_l1_provider/src/lib.rs
+++ b/crates/starknet_l1_provider/src/lib.rs
@@ -1,5 +1,7 @@
 pub mod errors;
 
+use std::fmt::Display;
+
 use starknet_api::executable_transaction::L1HandlerTransaction;
 use starknet_api::transaction::TransactionHash;
 
@@ -7,8 +9,13 @@ use crate::errors::L1ProviderError;
 
 type L1ProviderResult<T> = Result<T, L1ProviderError>;
 
+#[cfg(test)]
+#[path = "l1_provider_tests.rs"]
+pub mod l1_provider_tests;
+
 // TODO: optimistic proposer support, will add later to keep things simple, but the design here
 // is compatible with it.
+#[derive(Debug, Default)]
 pub struct L1Provider {
     unconsumed_l1_not_in_l2_block_txs: PendingMessagesFromL1,
     state: ProviderState,
@@ -53,8 +60,9 @@ impl L1Provider {
         todo!("Sets internal state as validate, returns error if state is Pending.")
     }
 
-    pub fn proposal_start(&mut self) {
-        todo!("Similar to validation_start.")
+    pub fn proposal_start(&mut self) -> L1ProviderResult<()> {
+        self.state = self.state.transition_to_propose()?;
+        Ok(())
     }
 
     /// Simple recovery from L1 and L2 reorgs by reseting the service, which rewinds L1 and L2
@@ -81,6 +89,7 @@ impl L1Provider {
     }
 }
 
+#[derive(Debug, Default)]
 struct PendingMessagesFromL1;
 
 impl PendingMessagesFromL1 {
@@ -90,7 +99,7 @@ impl PendingMessagesFromL1 {
 }
 
 /// Current state of the provider, where pending means: idle, between proposal/validation cycles.
-#[derive(Debug, Default)]
+#[derive(Clone, Copy, Debug, Default)]
 pub enum ProviderState {
     #[default]
     Pending,
@@ -99,8 +108,14 @@ pub enum ProviderState {
 }
 
 impl ProviderState {
-    fn _transition_to_propose(self) -> L1ProviderResult<Self> {
-        todo!()
+    fn transition_to_propose(self) -> L1ProviderResult<Self> {
+        match self {
+            ProviderState::Pending => Ok(ProviderState::Propose),
+            _ => Err(L1ProviderError::UnexpectedProviderStateTransition {
+                from: self,
+                to: ProviderState::Propose,
+            }),
+        }
     }
 
     fn _transition_to_validate(self) -> L1ProviderResult<Self> {
@@ -110,6 +125,21 @@ impl ProviderState {
     fn _transition_to_pending(self) -> L1ProviderResult<Self> {
         todo!()
     }
+
+    pub fn as_str(&self) -> &str {
+        match self {
+            ProviderState::Pending => "Pending",
+            ProviderState::Propose => "Propose",
+            ProviderState::Validate => "Validate",
+        }
+    }
+}
+
+impl Display for ProviderState {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(self.as_str())
+    }
 }
 
+#[derive(Debug)]
 pub struct L1ProviderConfig;
diff --git a/crates/starknet_mempool/src/mempool.rs b/crates/starknet_mempool/src/mempool.rs
index 22758b1b02..13899acd45 100644
--- a/crates/starknet_mempool/src/mempool.rs
+++ b/crates/starknet_mempool/src/mempool.rs
@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use std::fmt::Display;
 
 use starknet_api::block::GasPrice;
 use starknet_api::core::{ContractAddress, Nonce};
@@ -355,7 +356,7 @@ impl TransactionReference {
     }
 }
 
-impl std::fmt::Display for TransactionReference {
+impl Display for TransactionReference {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let TransactionReference { address, nonce, tx_hash, tip, max_l2_gas_price } = self;
         write!(