SERVER-19182 Integrate storage engine optimizations into $sample stage

1 files changed, 46 insertions, 0 deletions

diff --git a/src/mongo/platform/random_test.cpp b/src/mongo/platform/random_test.cpp
index 3aecfb2e98b..c4e214f1af9 100644
--- a/src/mongo/platform/random_test.cpp
+++ b/src/mongo/platform/random_test.cpp
@@ -98,6 +98,52 @@ TEST(RandomTest, R2) {
     ASSERT_EQUALS(100U, s.size());
 }
 
+/**
+ * Test that if two PsuedoRandom's have the same seed, then subsequent calls to
+ * nextCanonicalDouble() will return the same value.
+ */
+TEST(RandomTest, NextCanonicalSameSeed) {
+    PseudoRandom a(12);
+    PseudoRandom b(12);
+    for (int i = 0; i < 100; i++) {
+        ASSERT_EQUALS(a.nextCanonicalDouble(), b.nextCanonicalDouble());
+    }
+}
+
+/**
+ * Test that if two PsuedoRandom's have different seeds, then nextCanonicalDouble() will return
+ * different values.
+ */
+TEST(RandomTest, NextCanonicalDifferentSeeds) {
+    PseudoRandom a(12);
+    PseudoRandom b(11);
+    ASSERT_NOT_EQUALS(a.nextCanonicalDouble(), b.nextCanonicalDouble());
+}
+
+/**
+ * Test that nextCanonicalDouble() avoids returning a value soon after it has previously returned
+ * that value.
+ */
+TEST(RandomTest, NextCanonicalDistinctValues) {
+    PseudoRandom a(11);
+    std::set<double> s;
+    for (int i = 0; i < 100; i++) {
+        s.insert(a.nextCanonicalDouble());
+    }
+    ASSERT_EQUALS(100U, s.size());
+}
+
+/**
+ * Test that nextCanonicalDouble() always returns values between 0 and 1.
+ */
+TEST(RandomTest, NextCanonicalWithinRange) {
+    PseudoRandom prng(10);
+    for (int i = 0; i < 100; i++) {
+        double next = prng.nextCanonicalDouble();
+        ASSERT_LTE(0.0, next);
+        ASSERT_LT(next, 1.0);
+    }
+}
 
 TEST(RandomTest, Secure1) {
     SecureRandom* a = SecureRandom::create();