diff --git a/CHANGELOG.md b/CHANGELOG.md
index 17b2b7b..9e99e85 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,5 +10,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added a simple monobit test.
 - Added a block frequency test.
+- Added a runs test.
 
 [Unreleased]: https://git.chir.rs/ProcyOS/rand_testsuite
diff --git a/src/lib.rs b/src/lib.rs
index 454c940..95bc39f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@ use bitvec::{order::BitOrder, slice::BitSlice, store::BitStore};
 mod rand_core;
 
 pub mod tests;
+pub(crate) mod utils;
 
 #[cfg(feature = "rand_core")]
 pub use rand_core::RandomTestExt;
diff --git a/src/tests.rs b/src/tests.rs
index e4c6a95..e5c8c3f 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -2,12 +2,14 @@
 
 mod block_frequency;
 mod monobit;
+mod runs;
 
 use core::f64;
 
 use bitvec::prelude::{BitOrder, BitSlice, BitStore};
 pub use block_frequency::*;
 pub use monobit::*;
+pub use runs::*;
 
 use crate::RandomTest;
 
@@ -31,15 +33,20 @@ impl RandomTest for CombinedRandomTest {
     const RECOMMENDED_BIT_SIZE: usize = max_of([
         Monobit::RECOMMENDED_BIT_SIZE,
         BlockFrequency::RECOMMENDED_BIT_SIZE,
+        Runs::RECOMMENDED_BIT_SIZE,
     ]);
 
-    const MINIMUM_BIT_SIZE: usize =
-        max_of([Monobit::MINIMUM_BIT_SIZE, BlockFrequency::MINIMUM_BIT_SIZE]);
+    const MINIMUM_BIT_SIZE: usize = max_of([
+        Monobit::MINIMUM_BIT_SIZE,
+        BlockFrequency::MINIMUM_BIT_SIZE,
+        Runs::MINIMUM_BIT_SIZE,
+    ]);
 
     fn evaluate<T: BitStore, O: BitOrder>(&self, bs: &BitSlice<T, O>) -> Option<f64> {
         let mut worst_test_score = f64::MAX;
         worst_test_score = worst_test_score.min(Monobit.evaluate(bs)?);
         worst_test_score = worst_test_score.min(BlockFrequency.evaluate(bs)?);
+        worst_test_score = worst_test_score.min(Runs.evaluate(bs)?);
         Some(worst_test_score)
     }
 }
diff --git a/src/tests/block_frequency.rs b/src/tests/block_frequency.rs
index 5fb0361..f703e38 100644
--- a/src/tests/block_frequency.rs
+++ b/src/tests/block_frequency.rs
@@ -5,7 +5,7 @@ use extra_math::gamma::Gamma;
 #[allow(unused_imports, reason = "redundant in std use cases")]
 use num_traits::Float;
 
-use crate::RandomTest;
+use crate::{utils::ones_proportion, RandomTest};
 
 /// The Block Frequency Test splits the input data into multiple blocks, counts the frequency 1s and 0s within these blocks, and determines whether these are distributed well.
 ///
@@ -26,11 +26,7 @@ impl RandomTest for BlockFrequency {
         let block_count = bs.len() / block_size;
         let mut statistic = 0.0;
         for i in 0..block_count {
-            let one_count: usize = bs[i * block_size..(i + 1) * block_size]
-                .into_iter()
-                .map(|v| if *v { 1 } else { 0 })
-                .sum();
-            let pi = (one_count as f64) / (block_size as f64);
+            let pi = ones_proportion(&bs[i * block_size..(i + 1) * block_size]);
             statistic += (pi - 0.5).powi(2);
         }
         statistic *= (4 * block_size) as f64;
diff --git a/src/tests/runs.rs b/src/tests/runs.rs
new file mode 100644
index 0000000..0db9226
--- /dev/null
+++ b/src/tests/runs.rs
@@ -0,0 +1,67 @@
+//! Runs test code
+
+use bitvec::{order::BitOrder, slice::BitSlice, store::BitStore};
+use libm::erfc;
+#[allow(unused_imports, reason = "redundant in std use cases")]
+use num_traits::Float;
+
+use crate::{utils::ones_proportion, RandomTest};
+
+/// The runs test counts the number of bit transitions inside of a random number generator.
+///
+/// This test is defined in the [NIST Special Publication 800-22](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-22r1a.pdf).
+#[derive(Copy, Clone, Debug)]
+pub struct Runs;
+
+impl RandomTest for Runs {
+    const RECOMMENDED_BIT_SIZE: usize = 100;
+    const MINIMUM_BIT_SIZE: usize = 2;
+
+    fn evaluate<T: BitStore, O: BitOrder>(&self, bs: &BitSlice<T, O>) -> Option<f64> {
+        if bs.len() < Self::MINIMUM_BIT_SIZE {
+            return None;
+        }
+        let pi = ones_proportion(bs);
+        if (pi - 0.5).abs() > 2.0 / (bs.len() as f64).sqrt() {
+            return Some(0.0);
+        }
+        let (_, runs) = bs
+            .into_iter()
+            .skip(1)
+            .fold((bs[0], 1usize), |(last, cum), cur| {
+                if *cur == last {
+                    (last, cum)
+                } else {
+                    (*cur, cum + 1)
+                }
+            });
+
+        Some(erfc(
+            (runs as f64 - 2.0 * (bs.len() as f64) * pi * (1.0 - pi)).abs()
+                / (2.0 * (2.0 * bs.len() as f64).sqrt() * pi * (1.0 - pi)),
+        ))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use bitvec::prelude::*;
+
+    use crate::RandomTest;
+
+    use super::Runs;
+
+    #[test]
+    fn runs_test_vector() {
+        let epsilon = bitvec![
+            1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0,
+            0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0,
+            1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1,
+            0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0
+        ];
+        let res = Runs.evaluate(epsilon.as_bitslice());
+        assert!(res.is_some());
+        let res = res.unwrap();
+        assert!(res > 0.01, "Data should be evaluated as random");
+    }
+}
diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644
index 0000000..98a2fc4
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,10 @@
+//! Various utility functions
+
+use core::convert::identity;
+
+use bitvec::{order::BitOrder, slice::BitSlice, store::BitStore};
+
+/// Calculates the proportion of ones in a bitslice
+pub fn ones_proportion<B: BitStore, O: BitOrder>(bs: &BitSlice<B, O>) -> f64 {
+    bs.into_iter().filter(|b| **b).count() as f64 / bs.len() as f64
+}