diff --git a/consensus/src/dag/mod.rs b/consensus/src/dag/mod.rs
index 106c1c9c..a38f306a 100644
--- a/consensus/src/dag/mod.rs
+++ b/consensus/src/dag/mod.rs
@@ -362,14 +362,14 @@ mod test {
         let forker_id = NodeIndex(3);
         let keychain = keychains.get(forker_id.0).expect("we have the keychain");
         let unit = random_full_parent_units_up_to(0, node_count, session_id)
-            .get(0)
+            .first()
             .expect("we have initial units")
             .get(forker_id.0)
             .expect("We have the forker")
             .clone();
         let unit = Signed::sign(unit, keychain);
         let mut fork = random_full_parent_units_up_to(0, node_count, session_id)
-            .get(0)
+            .first()
             .expect("we have initial units")
             .get(forker_id.0)
             .expect("We have the forker")
@@ -377,7 +377,7 @@ mod test {
         // we might have randomly created an identical "fork"
         while fork.hash() == unit.hash() {
             fork = random_full_parent_units_up_to(0, node_count, session_id)
-                .get(0)
+                .first()
                 .expect("we have initial units")
                 .get(forker_id.0)
                 .expect("We have the forker")
diff --git a/consensus/src/dag/reconstruction/dag.rs b/consensus/src/dag/reconstruction/dag.rs
index c22159c0..e488b49c 100644
--- a/consensus/src/dag/reconstruction/dag.rs
+++ b/consensus/src/dag/reconstruction/dag.rs
@@ -145,7 +145,7 @@ mod test {
     ) -> Vec<Vec<ReconstructedUnit<TestingFullUnit>>> {
         let hashes: Vec<_> = dag.iter().map(unit_hashes).collect();
         let initial_units: Vec<_> = dag
-            .get(0)
+            .first()
             .expect("only called on nonempty dags")
             .iter()
             .map(|unit| ReconstructedUnit::initial(unit.clone()))
diff --git a/consensus/src/dag/reconstruction/mod.rs b/consensus/src/dag/reconstruction/mod.rs
index 5a44b648..ec7b8c1e 100644
--- a/consensus/src/dag/reconstruction/mod.rs
+++ b/consensus/src/dag/reconstruction/mod.rs
@@ -290,7 +290,7 @@ mod test {
     fn requests_single_parent() {
         let mut reconstruction = Reconstruction::new();
         let dag = random_full_parent_units_up_to(1, NodeCount(4), 43);
-        for unit in dag.get(0).expect("just created").iter().skip(1) {
+        for unit in dag.first().expect("just created").iter().skip(1) {
             reconstruction.add_unit(unit.clone());
         }
         let unit = dag
@@ -335,7 +335,7 @@ mod test {
         let node_count = NodeCount(7);
         let mut reconstruction = Reconstruction::new();
         let dag = random_full_parent_units_up_to(0, node_count, 43);
-        for unit in dag.get(0).expect("just created") {
+        for unit in dag.first().expect("just created") {
             reconstruction.add_unit(unit.clone());
         }
         let other_dag = random_full_parent_units_up_to(1, node_count, 43);
@@ -353,7 +353,7 @@ mod test {
             &Request::ParentsOf(unit_hash),
         );
         let parent_hashes: HashMap<_, _> = other_dag
-            .get(0)
+            .first()
             .expect("other dag has initial units")
             .iter()
             .map(|unit| (unit.coord(), unit.hash()))
diff --git a/consensus/src/dag/reconstruction/parents.rs b/consensus/src/dag/reconstruction/parents.rs
index 8fb6fcd5..ac1ea954 100644
--- a/consensus/src/dag/reconstruction/parents.rs
+++ b/consensus/src/dag/reconstruction/parents.rs
@@ -294,7 +294,7 @@ mod test {
     fn requests_single_parent() {
         let mut reconstruction = Reconstruction::new();
         let dag = random_full_parent_units_up_to(1, NodeCount(4), 43);
-        for unit in dag.get(0).expect("just created").iter().skip(1) {
+        for unit in dag.first().expect("just created").iter().skip(1) {
             reconstruction.add_unit(unit.clone());
         }
         let unit = dag
@@ -316,7 +316,7 @@ mod test {
         let mut reconstruction = Reconstruction::new();
         let mut dag = random_full_parent_units_up_to(7, NodeCount(4), 43);
         dag.reverse();
-        for unit in dag.get(0).expect("we have the top units") {
+        for unit in dag.first().expect("we have the top units") {
             let ReconstructionResult { units, requests } = reconstruction.add_unit(unit.clone());
             assert!(units.is_empty());
             assert_eq!(requests.len(), 4);
@@ -341,7 +341,7 @@ mod test {
     fn handles_bad_hash() {
         let mut reconstruction = Reconstruction::new();
         let dag = random_full_parent_units_up_to(0, NodeCount(4), 43);
-        for unit in dag.get(0).expect("just created") {
+        for unit in dag.first().expect("just created") {
             reconstruction.add_unit(unit.clone());
         }
         let other_dag = random_full_parent_units_up_to(1, NodeCount(4), 43);
@@ -359,7 +359,7 @@ mod test {
             &Request::ParentsOf(unit_hash),
         );
         let parent_hashes: HashMap<_, _> = other_dag
-            .get(0)
+            .first()
             .expect("other dag has initial units")
             .iter()
             .map(|unit| (unit.coord(), unit.hash()))
diff --git a/consensus/src/dag/validation.rs b/consensus/src/dag/validation.rs
index 65f5c62e..66f63547 100644
--- a/consensus/src/dag/validation.rs
+++ b/consensus/src/dag/validation.rs
@@ -224,9 +224,9 @@ mod test {
         let store = UnitStore::<WrappedSignedUnit>::new(node_count);
         let mut validator = Validator::new(UnitValidator::new(session_id, keychains[0], max_round));
         let unit = random_full_parent_units_up_to(0, node_count, session_id)
-            .get(0)
+            .first()
             .expect("we have the first round")
-            .get(0)
+            .first()
             .expect("we have the initial unit for the zeroth creator")
             .clone();
         let unit = Signed::sign(unit, &keychains[0]);
@@ -252,9 +252,9 @@ mod test {
         let mut store = UnitStore::new(node_count);
         let mut validator = Validator::new(UnitValidator::new(session_id, keychains[0], max_round));
         let unit = random_full_parent_units_up_to(0, node_count, session_id)
-            .get(0)
+            .first()
             .expect("we have the first round")
-            .get(0)
+            .first()
             .expect("we have the initial unit for the zeroth creator")
             .clone();
         let unit = Signed::sign(unit, &keychains[0]);
@@ -290,7 +290,7 @@ mod test {
         let fork = random_full_parent_units_up_to(2, node_count, session_id)
             .get(2)
             .expect("we have the requested round")
-            .get(0)
+            .first()
             .expect("we have the unit for the zeroth creator")
             .clone();
         let fork = Signed::sign(fork, &keychains[0]);
@@ -322,7 +322,7 @@ mod test {
         let fork = random_full_parent_units_up_to(2, node_count, session_id)
             .get(2)
             .expect("we have the requested round")
-            .get(0)
+            .first()
             .expect("we have the unit for the zeroth creator")
             .clone();
         let fork = Signed::sign(fork, &keychains[0]);
@@ -347,7 +347,7 @@ mod test {
         let fork = random_full_parent_units_up_to(2, node_count, session_id)
             .get(2)
             .expect("we have the requested round")
-            .get(0)
+            .first()
             .expect("we have the unit for the zeroth creator")
             .clone();
         let fork = Signed::sign(fork, &keychains[0]);
@@ -395,7 +395,7 @@ mod test {
         let fork = random_full_parent_units_up_to(2, node_count, session_id)
             .get(2)
             .expect("we have the requested round")
-            .get(0)
+            .first()
             .expect("we have the unit for the zeroth creator")
             .clone();
         let fork = Signed::sign(fork, &keychains[0]);
diff --git a/consensus/src/testing/dag.rs b/consensus/src/testing/dag.rs
index 6e43d07e..770fa628 100644
--- a/consensus/src/testing/dag.rs
+++ b/consensus/src/testing/dag.rs
@@ -77,7 +77,7 @@ impl DagFeeder {
     ) -> DagFeeder {
         let units_map = units.iter().map(|u| (u.hash(), u.clone())).collect();
         let node_count = units
-            .get(0)
+            .first()
             .expect("we have at least one unit")
             .unit
             .control_hash()
diff --git a/consensus/src/units/store.rs b/consensus/src/units/store.rs
index ee7b3474..e04adea8 100644
--- a/consensus/src/units/store.rs
+++ b/consensus/src/units/store.rs
@@ -145,9 +145,9 @@ mod test {
         let node_count = NodeCount(7);
         let mut store = UnitStore::new(node_count);
         let unit = random_full_parent_units_up_to(0, node_count, 43)
-            .get(0)
+            .first()
             .expect("we have the first round")
-            .get(0)
+            .first()
             .expect("we have the initial unit for the zeroth creator")
             .clone();
         store.insert(unit.clone());
@@ -174,9 +174,9 @@ mod test {
         let variants: HashSet<_> = (0..15)
             .map(|_| {
                 random_full_parent_units_up_to(0, node_count, 43)
-                    .get(0)
+                    .first()
                     .expect("we have the first round")
-                    .get(0)
+                    .first()
                     .expect("we have the initial unit for the zeroth creator")
                     .clone()
             })
@@ -188,7 +188,7 @@ mod test {
         for unit in &variants {
             assert_eq!(store.unit(&unit.hash()), Some(unit));
         }
-        let canonical_unit = variants.get(0).expect("we have the unit").clone();
+        let canonical_unit = variants.first().expect("we have the unit").clone();
         assert_eq!(
             store.canonical_unit(canonical_unit.coord()),
             Some(&canonical_unit)