diff --git a/CourseApp.Tests/CourseApp.Tests.csproj b/CourseApp.Tests/CourseApp.Tests.csproj
index 8fb7e4a..e253b4b 100644
--- a/CourseApp.Tests/CourseApp.Tests.csproj
+++ b/CourseApp.Tests/CourseApp.Tests.csproj
@@ -9,6 +9,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
+    <PackageReference Include="Moq" Version="4.15.2" />
     <PackageReference Include="xunit" Version="2.4.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
     <PackageReference Include="StyleCop.Analyzers" Version="1.0.2" PrivateAssets="all" />
diff --git a/CourseApp.Tests/DemoTest.cs b/CourseApp.Tests/DemoTest.cs
index fdc46f5..618bfb0 100644
--- a/CourseApp.Tests/DemoTest.cs
+++ b/CourseApp.Tests/DemoTest.cs
@@ -1,14 +1,53 @@
 using System;
 using Xunit;
+using Moq;
 
 namespace CourseApp.Tests
 {
     public class DemoTest
     {
+        [Theory]
+        [InlineData(5, 5, 10)]
+        [InlineData(-5, -5, -10)]
+        [InlineData(-5, 5, 0)]
+        [InlineData(0, 0, 0)]
+        public void TestCalc(int x, int y, int exp)
+        {
+            Numer a = new Numer();
+            a.Value = x;
+            Numer b = new Numer();
+            b.Value = y;
+            Assert.Equal(exp, Program.Calc(a, b));
+        }
+
+        [Fact]
+        public void TestForOneNull()
+        {
+            Numer a = new Numer();
+            Numer b = new Numer();
+            a.Value = null;
+            b.Value = 1;
+            Assert.Throws<System.NullReferenceException>(() => Program.Calc(a, b));
+        }
+
+        [Fact]
+        public void TestForNull()
+        {
+            Numer a = new Numer();
+            Numer b = new Numer();
+            a.Value = null;
+            b.Value = null;
+            Assert.Throws<System.NullReferenceException>(() => Program.Calc(a, b));
+        }
+
         [Fact]
-        public void Test1()
+        public void TestFuntionRun()
         {
-            Assert.True(true);
+            var mock = new Mock<ClassB>();
+            mock.Setup(b => b.B(It.IsAny<int>()));
+            var classA = new ClassA(mock.Object);
+            var exp = classA.B();
+            mock.Verify(b => b.B(It.IsAny<int>()), Times.Once());
         }
     }
 }
diff --git a/CourseApp/ClassA.cs b/CourseApp/ClassA.cs
new file mode 100644
index 0000000..6da70a5
--- /dev/null
+++ b/CourseApp/ClassA.cs
@@ -0,0 +1,20 @@
+using System;
+
+namespace CourseApp
+{
+    public class ClassA
+    {
+        private int a = 0;
+        private ClassB b = new ClassB();
+
+        public ClassA(ClassB b)
+        {
+            this.b = b;
+        }
+
+        public int B()
+        {
+            return this.b.B(a);
+        }
+    }
+}
\ No newline at end of file
diff --git a/CourseApp/ClassB.cs b/CourseApp/ClassB.cs
new file mode 100644
index 0000000..8a3bc34
--- /dev/null
+++ b/CourseApp/ClassB.cs
@@ -0,0 +1,13 @@
+using System;
+
+namespace CourseApp
+{
+    public class ClassB
+    {
+        public virtual int B(int a)
+        {
+            a++;
+            return a;
+        }
+    }
+}
\ No newline at end of file
diff --git a/CourseApp/Numer.cs b/CourseApp/Numer.cs
new file mode 100644
index 0000000..8d749db
--- /dev/null
+++ b/CourseApp/Numer.cs
@@ -0,0 +1,9 @@
+using System;
+
+namespace CourseApp
+{
+    public class Numer
+    {
+        public object Value { get; set; }
+    }
+}
diff --git a/CourseApp/Program.cs b/CourseApp/Program.cs
index 248bbe4..f482ee4 100644
--- a/CourseApp/Program.cs
+++ b/CourseApp/Program.cs
@@ -4,9 +4,34 @@ namespace CourseApp
 {
     public class Program
     {
+        public static int Calc(Numer a, Numer b)
+        {
+            if ((a.Value == null) || (b.Value == null))
+            {
+                throw new NullReferenceException("a or b is null");
+            }
+            else
+            {
+                int c = (int)a.Value + (int)b.Value;
+                return c;
+            }
+        }
+
+        public static void Task2()
+        {
+            ClassB b = new ClassB();
+            ClassA a = new ClassA(b);
+            Console.WriteLine(a.B());
+        }
+
         public static void Main(string[] args)
         {
-            Console.WriteLine("Hello World!");
+            Numer a = new Numer();
+            Numer b = new Numer();
+            a.Value = 5;
+            b.Value = 5;
+            Console.WriteLine(Program.Calc(a, b));
+            Task2();
             Console.ReadLine();
         }
     }