diff --git a/csharp/Platform.Random.Tests/RandomExtensionsTests.cs b/csharp/Platform.Random.Tests/RandomExtensionsTests.cs
index 819c462..1d0e03b 100644
--- a/csharp/Platform.Random.Tests/RandomExtensionsTests.cs
+++ b/csharp/Platform.Random.Tests/RandomExtensionsTests.cs
@@ -1,9 +1,150 @@
+using System.Linq;
+using Platform.Ranges;
 using Xunit;
 
 namespace Platform.Random.Tests
 {
     public class RandomExtensionsTests
     {
+        [Fact]
+        public void NextUInt64_WithoutRange_ReturnsValidValues()
+        {
+            var random = new System.Random(42);
+            var values = new ulong[100];
+            
+            for (var i = 0; i < values.Length; i++)
+            {
+                values[i] = random.NextUInt64();
+                Assert.InRange(values[i], ulong.MinValue, ulong.MaxValue);
+            }
+            
+            var uniqueValues = values.Distinct().Count();
+            Assert.True(uniqueValues > 50, "Should generate varied random values");
+        }
+
+        [Fact]
+        public void NextUInt64_WithRange_ReturnsValuesInRange()
+        {
+            var random = new System.Random(42);
+            var range = new Range<ulong>(10UL, 20UL);
+            
+            for (var i = 0; i < 100; i++)
+            {
+                var value = random.NextUInt64(range);
+                Assert.InRange(value, range.Minimum, range.Maximum);
+            }
+        }
+
+        [Fact]
+        public void NextUInt64_WithMinimumRange_ReturnsMinimumValue()
+        {
+            var random = new System.Random(42);
+            var range = new Range<ulong>(5UL, 5UL);
+            
+            var value = random.NextUInt64(range);
+            Assert.Equal(5UL, value);
+        }
+
+        [Fact]
+        public void NextUInt64_WithLargeRange_ReturnsValidValues()
+        {
+            var random = new System.Random(42);
+            var range = new Range<ulong>(ulong.MaxValue - 1000UL, ulong.MaxValue);
+            
+            for (var i = 0; i < 10; i++)
+            {
+                var value = random.NextUInt64(range);
+                Assert.InRange(value, range.Minimum, range.Maximum);
+            }
+        }
+
+        [Fact]
+        public void NextUInt64_WithZeroRange_ReturnsZero()
+        {
+            var random = new System.Random(42);
+            var range = new Range<ulong>(0UL, 0UL);
+            
+            var value = random.NextUInt64(range);
+            Assert.Equal(0UL, value);
+        }
+
+        [Fact]
+        public void NextUInt64_WithDifferentSeeds_GeneratesDifferentSequences()
+        {
+            var random1 = new System.Random(1);
+            var random2 = new System.Random(2);
+            var range = new Range<ulong>(0UL, 1000UL);
+            
+            var values1 = new ulong[10];
+            var values2 = new ulong[10];
+            
+            for (var i = 0; i < 10; i++)
+            {
+                values1[i] = random1.NextUInt64(range);
+                values2[i] = random2.NextUInt64(range);
+            }
+            
+            Assert.NotEqual(values1, values2);
+        }
+
+        [Fact]
+        public void NextBoolean_GeneratesBothTrueAndFalse()
+        {
+            var random = new System.Random(42);
+            var trueCount = 0;
+            var falseCount = 0;
+            
+            for (var i = 0; i < 1000; i++)
+            {
+                var value = random.NextBoolean();
+                if (value)
+                {
+                    trueCount++;
+                }
+                else
+                {
+                    falseCount++;
+                }
+            }
+            
+            Assert.True(trueCount > 0, "Should generate at least one true value");
+            Assert.True(falseCount > 0, "Should generate at least one false value");
+            Assert.InRange(trueCount, 300, 700);
+            Assert.InRange(falseCount, 300, 700);
+        }
+
+        [Fact]
+        public void NextBoolean_WithSameSeed_GeneratesSameSequence()
+        {
+            var random1 = new System.Random(123);
+            var random2 = new System.Random(123);
+            
+            for (var i = 0; i < 10; i++)
+            {
+                var value1 = random1.NextBoolean();
+                var value2 = random2.NextBoolean();
+                Assert.Equal(value1, value2);
+            }
+        }
+
+        [Fact]
+        public void NextBoolean_WithDifferentSeeds_GeneratesDifferentSequences()
+        {
+            var random1 = new System.Random(1);
+            var random2 = new System.Random(2);
+            
+            var values1 = new bool[20];
+            var values2 = new bool[20];
+            
+            for (var i = 0; i < 20; i++)
+            {
+                values1[i] = random1.NextBoolean();
+                values2[i] = random2.NextBoolean();
+            }
+            
+            Assert.NotEqual(values1, values2);
+        }
+
         [Fact]
         public void NextUInt64Test()
         {
diff --git a/csharp/Platform.Random.Tests/RandomHelpersTests.cs b/csharp/Platform.Random.Tests/RandomHelpersTests.cs
index 4f47704..1c4bb31 100644
--- a/csharp/Platform.Random.Tests/RandomHelpersTests.cs
+++ b/csharp/Platform.Random.Tests/RandomHelpersTests.cs
@@ -1,9 +1,58 @@
+using System.Linq;
 using Xunit;
 
 namespace Platform.Random.Tests
 {
     public class RandomHelpersTests
     {
+        [Fact]
+        public void Default_IsNotNull()
+        {
+            Assert.NotNull(RandomHelpers.Default);
+        }
+
+        [Fact]
+        public void Default_IsSameInstance()
+        {
+            var instance1 = RandomHelpers.Default;
+            var instance2 = RandomHelpers.Default;
+            
+            Assert.Same(instance1, instance2);
+        }
+
+        [Fact]
+        public void Default_IsRandomInstance()
+        {
+            Assert.IsType<System.Random>(RandomHelpers.Default);
+        }
+
+        [Fact]
+        public void Default_GeneratesRandomValues()
+        {
+            var values = new int[100];
+            for (var i = 0; i < values.Length; i++)
+            {
+                values[i] = RandomHelpers.Default.Next();
+            }
+            
+            var uniqueValues = values.Distinct().Count();
+            Assert.True(uniqueValues > 50, "Should generate varied random values");
+        }
+
+        [Fact]
+        public void Default_NextMethodWorks()
+        {
+            var value = RandomHelpers.Default.Next(0, 100);
+            Assert.InRange(value, 0, 99);
+        }
+
+        [Fact]
+        public void Default_NextDoubleWorks()
+        {
+            var value = RandomHelpers.Default.NextDouble();
+            Assert.InRange(value, 0.0, 1.0);
+        }
+
         [Fact]
         public void DefaultFieldTest()
         {