3 files changed, 63 insertions, 18 deletions

diff --git a/tests/common/mod.rs b/tests/common/mod.rs
index 006f230..666f7f5 100644
--- a/tests/common/mod.rs
+++ b/tests/common/mod.rs
@@ -12,7 +12,19 @@ fn test_zero() {
     getrandom_impl(&mut [0u8; 0]).unwrap();
 }
 
+// Return the number of bits in which s1 and s2 differ
+#[cfg(not(feature = "custom"))]
+fn num_diff_bits(s1: &[u8], s2: &[u8]) -> usize {
+    assert_eq!(s1.len(), s2.len());
+    s1.iter()
+        .zip(s2.iter())
+        .map(|(a, b)| (a ^ b).count_ones() as usize)
+        .sum()
+}
+
+// Tests the quality of calling getrandom on two large buffers
 #[test]
+#[cfg(not(feature = "custom"))]
 fn test_diff() {
     let mut v1 = [0u8; 1000];
     getrandom_impl(&mut v1).unwrap();
@@ -20,13 +32,35 @@ fn test_diff() {
     let mut v2 = [0u8; 1000];
     getrandom_impl(&mut v2).unwrap();
 
-    let mut n_diff_bits = 0;
-    for i in 0..v1.len() {
-        n_diff_bits += (v1[i] ^ v2[i]).count_ones();
-    }
+    // Between 3.5 and 4.5 bits per byte should differ. Probability of failure:
+    // ~ 2^(-94) = 2 * CDF[BinomialDistribution[8000, 0.5], 3500]
+    let d = num_diff_bits(&v1, &v2);
+    assert!(d > 3500);
+    assert!(d < 4500);
+}
 
-    // Check at least 1 bit per byte differs. p(failure) < 1e-1000 with random input.
-    assert!(n_diff_bits >= v1.len() as u32);
+// Tests the quality of calling getrandom repeatedly on small buffers
+#[test]
+#[cfg(not(feature = "custom"))]
+fn test_small() {
+    // For each buffer size, get at least 256 bytes and check that between
+    // 3 and 5 bits per byte differ. Probability of failure:
+    // ~ 2^(-91) = 64 * 2 * CDF[BinomialDistribution[8*256, 0.5], 3*256]
+    for size in 1..=64 {
+        let mut num_bytes = 0;
+        let mut diff_bits = 0;
+        while num_bytes < 256 {
+            let mut s1 = vec![0u8; size];
+            getrandom_impl(&mut s1).unwrap();
+            let mut s2 = vec![0u8; size];
+            getrandom_impl(&mut s2).unwrap();
+
+            num_bytes += size;
+            diff_bits += num_diff_bits(&s1, &s2);
+        }
+        assert!(diff_bits > 3 * num_bytes);
+        assert!(diff_bits < 5 * num_bytes);
+    }
 }
 
 #[test]
diff --git a/tests/custom.rs b/tests/custom.rs
index 62eae1d..b085094 100644
--- a/tests/custom.rs
+++ b/tests/custom.rs
@@ -7,13 +7,8 @@
 ))]
 
 use wasm_bindgen_test::wasm_bindgen_test as test;
-#[cfg(feature = "test-in-browser")]
-wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);
 
-use core::{
-    num::NonZeroU32,
-    sync::atomic::{AtomicU8, Ordering},
-};
+use core::num::NonZeroU32;
 use getrandom::{getrandom, register_custom_getrandom, Error};
 
 fn len7_err() -> Error {
@@ -21,27 +16,36 @@ fn len7_err() -> Error {
 }
 
 fn super_insecure_rng(buf: &mut [u8]) -> Result<(), Error> {
+    // `getrandom` guarantees it will not call any implementation if the output
+    // buffer is empty.
+    assert!(!buf.is_empty());
     // Length 7 buffers return a custom error
     if buf.len() == 7 {
         return Err(len7_err());
     }
-    // Otherwise, increment an atomic counter
-    static COUNTER: AtomicU8 = AtomicU8::new(0);
+    // Otherwise, fill bytes based on input length
+    let mut start = buf.len() as u8;
     for b in buf {
-        *b = COUNTER.fetch_add(1, Ordering::Relaxed);
+        *b = start;
+        start = start.wrapping_mul(3);
     }
     Ok(())
 }
 
 register_custom_getrandom!(super_insecure_rng);
 
+use getrandom::getrandom as getrandom_impl;
+mod common;
+
 #[test]
 fn custom_rng_output() {
     let mut buf = [0u8; 4];
     assert_eq!(getrandom(&mut buf), Ok(()));
-    assert_eq!(buf, [0, 1, 2, 3]);
+    assert_eq!(buf, [4, 12, 36, 108]);
+
+    let mut buf = [0u8; 3];
     assert_eq!(getrandom(&mut buf), Ok(()));
-    assert_eq!(buf, [4, 5, 6, 7]);
+    assert_eq!(buf, [3, 9, 27]);
 }
 
 #[test]
diff --git a/tests/rdrand.rs b/tests/rdrand.rs
index 4ff85c4..a355c31 100644
--- a/tests/rdrand.rs
+++ b/tests/rdrand.rs
@@ -6,10 +6,17 @@
 use getrandom::Error;
 #[macro_use]
 extern crate cfg_if;
+#[path = "../src/lazy.rs"]
+mod lazy;
 #[path = "../src/rdrand.rs"]
 mod rdrand;
 #[path = "../src/util.rs"]
 mod util;
 
-use rdrand::getrandom_inner as getrandom_impl;
+// The rdrand implementation has the signature of getrandom_uninit(), but our
+// tests expect getrandom_impl() to have the signature of getrandom().
+fn getrandom_impl(dest: &mut [u8]) -> Result<(), Error> {
+    rdrand::getrandom_inner(unsafe { util::slice_as_uninit_mut(dest) })?;
+    Ok(())
+}
 mod common;