diff --git a/src/NSrtm.Core.xTests/Spline3DCalculatorExternalDataTest.cs b/src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorExternalDataTest.cs
similarity index 93%
rename from src/NSrtm.Core.xTests/Spline3DCalculatorExternalDataTest.cs
rename to src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorExternalDataTest.cs
index 2752a15..087267b 100644
--- a/src/NSrtm.Core.xTests/Spline3DCalculatorExternalDataTest.cs
+++ b/src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorExternalDataTest.cs
@@ -2,9 +2,9 @@
 using NSrtm.Core.BicubicInterpolation;
 using Xunit;
 
-namespace NSrtm.Core.xTests
+namespace NSrtm.Core.xTests.BicubicInterpolation
 {
-    public class Spline3DCalculatorExternalDataTest
+    public class BicubicCalculatorExternalDataTest
     {
         [Theory]
         [MemberData("ExternalData")]
diff --git a/src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorSimplePlaneTests.cs b/src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorSimplePlaneTests.cs
new file mode 100644
index 0000000..7a1522d
--- /dev/null
+++ b/src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorSimplePlaneTests.cs
@@ -0,0 +1,93 @@
+using System.Collections.Generic;
+using System.Linq;
+using NSrtm.Core.BicubicInterpolation;
+using Xunit;
+
+namespace NSrtm.Core.xTests.BicubicInterpolation
+{
+    public class BicubicCalculatorSimplePlaneTests
+    {
+        [Theory]
+        [MemberData("SimplePlane")]
+        public void BicubicSplineCalculatorReturnsSimilarResultForNodes(
+            List<List<double>> values,
+            double step)
+        {
+            var spline = BicubicCalculator.GetSpline(values, step);
+            var nodes = Enumerable.Range(0, 2);
+            var positions = nodes.SelectMany(x => nodes.Select(y => new {x, y}))
+                                 .ToList();
+            foreach (var position in positions)
+            {
+                var result = spline.Evaluate(position.x, position.y);
+                var expected = values[position.x + 1][position.y + 1];
+                AssertDeep.Equal(result, expected, config => config.DoublePrecision = 1e-5);
+            }
+        }
+
+        [Theory]
+        [MemberData("SimplePlane")]
+        public void BicubicSplineCalculatorReturnsCorrectResultsForSpaceBetweenNodes(
+            List<List<double>> values,
+            double step)
+        {
+            var spline = BicubicCalculator.GetSpline(values, step);
+            var nodes = Enumerable.Range(0, 11).Select(p=>p*0.1);
+            var positions = nodes.SelectMany(x => nodes.Select(y => new {x, y}))
+                                 .ToList();
+            var expected = values[0][0];
+            foreach (var position in positions)
+            {
+                var result = spline.Evaluate(position.x, position.y);
+                AssertDeep.Equal(result, expected, config => config.DoublePrecision = 1e-5);
+            }
+        }
+
+        #region Static Members
+
+        public static IReadOnlyList<object[]> SimplePlane
+        {
+            get
+            {
+                return new List<object[]>
+                       {
+                           new object[]
+                           {
+                               new List<List<double>>
+                               {
+                                   new List<double> {10, 10, 10, 10},
+                                   new List<double> {10, 10, 10, 10},
+                                   new List<double> {10, 10, 10, 10},
+                                   new List<double> {10, 10, 10, 10},
+                               },
+                               1
+                           },
+                           new object[]
+                           {
+                               new List<List<double>>
+                               {
+                                   new List<double> {-0.5, -0.5, -0.5, -0.5},
+                                   new List<double> {-0.5, -0.5, -0.5, -0.5},
+                                   new List<double> {-0.5, -0.5, -0.5, -0.5},
+                                   new List<double> {-0.5, -0.5, -0.5, -0.5},
+                               },
+                               1
+                           },
+                           new object[]
+                           {
+                               new List<List<double>>
+                               {
+                                   new List<double> {0, 0, 0, 0},
+                                   new List<double> {0, 0, 0, 0},
+                                   new List<double> {0, 0, 0, 0},
+                                   new List<double> {0, 0, 0, 0},
+                               },
+                               1
+                           }
+                       };
+            }
+        }
+
+        #endregion
+    }
+}
diff --git a/src/NSrtm.Core.xTests/Spline3DCalculatorSimpleTests.cs b/src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorWrongArgumentsTests.cs
similarity index 91%
rename from src/NSrtm.Core.xTests/Spline3DCalculatorSimpleTests.cs
rename to src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorWrongArgumentsTests.cs
index b1d1314..0e8f7e9 100644
--- a/src/NSrtm.Core.xTests/Spline3DCalculatorSimpleTests.cs
+++ b/src/NSrtm.Core.xTests/BicubicInterpolation/BicubicCalculatorWrongArgumentsTests.cs
@@ -3,9 +3,9 @@
 using NSrtm.Core.BicubicInterpolation;
 using Xunit;
 
-namespace NSrtm.Core.xTests
+namespace NSrtm.Core.xTests.BicubicInterpolation
 {
-    public class Spline3DCalculatorSimpleTests
+    public class BicubicCalculatorWrongArgumentsTests
     {
         [Fact]
         public void EmptyValuesContainerThrowsArgumentNullException()
@@ -14,7 +14,7 @@ public void EmptyValuesContainerThrowsArgumentNullException()
         }
 
         [Fact]
-        public void ValuesWithWrongSizeDimensionThrowsArgumentNullException()
+        public void ValuesWithWrongSizeDimensionThrowsArgumentException()
         {
             Assert.Throws<ArgumentException>(
                                                  () =>
@@ -29,7 +29,7 @@ public void ValuesWithWrongSizeDimensionThrowsArgumentNullException()
         }
 
         [Fact]
-        public void ZeroStepThrowsArgumentNullException()
+        public void ZeroStepThrowsArgumentOutOfRangeException()
         {
             Assert.Throws<ArgumentOutOfRangeException>(
                                                  () =>
@@ -44,7 +44,7 @@ public void ZeroStepThrowsArgumentNullException()
         }
 
         [Fact]
-        public void NegativeStepThrowsArgumentNullException()
+        public void NegativeStepThrowsArgumentOutOfRangeException()
         {
             Assert.Throws<ArgumentOutOfRangeException>(
                                                  () =>
diff --git a/src/NSrtm.Core.xTests/NSrtm.Core.xTests.csproj b/src/NSrtm.Core.xTests/NSrtm.Core.xTests.csproj
index c18b4a1..f1c2aaa 100644
--- a/src/NSrtm.Core.xTests/NSrtm.Core.xTests.csproj
+++ b/src/NSrtm.Core.xTests/NSrtm.Core.xTests.csproj
@@ -77,13 +77,14 @@
       <Link>Properties\GlobalAssemblyInfo.cs</Link>
     </Compile>
     <Compile Include="AssertDeep.cs" />
+    <Compile Include="BicubicInterpolation\BicubicCalculatorSimplePlaneTests.cs" />
     <Compile Include="CoordinatesNormalizationToEgmDatumTests.cs" />
     <Compile Include="PgmDataDescriptionExtractorTests.cs" />
     <Compile Include="PgmElevationProviderCoordinatesFindingTests.cs" />
     <Compile Include="PgmPreamblesHelper.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="Spline3DCalculatorSimpleTests.cs" />
-    <Compile Include="Spline3DCalculatorExternalDataTest.cs" />
+    <Compile Include="BicubicInterpolation\BicubicCalculatorWrongArgumentsTests.cs" />
+    <Compile Include="BicubicInterpolation\BicubicCalculatorExternalDataTest.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\NSrtm.Core\NSrtm.Core.csproj">