diff --git a/src/Triangle.Tests/Topology/OtriTest.cs b/src/Triangle.Tests/Topology/OtriTest.cs
new file mode 100644
index 0000000..a17eaeb
--- /dev/null
+++ b/src/Triangle.Tests/Topology/OtriTest.cs
@@ -0,0 +1,508 @@
+
+namespace TriangleNet.Tests
+{
+    using NUnit.Framework;
+    using TriangleNet.Geometry;
+    using TriangleNet.Topology;
+
+    // The Otri (orientent triangle) struct is the heart of Triangle's mesh
+    // datastructure. It basically represents one of the three edges of the
+    // triangle by associating an orientation to the triangle object.
+    //
+    // For testing, a minimal example mesh is considered. It consists of
+    // 6 vertices and 4 triangles.
+    //
+    // Vertices:
+    //    X [-2] [0] [2] [-1] [1] [0]
+    //    Y [ 0] [0] [0] [ 1] [1] [2]
+    //
+    // Triangles and neighbors and neighbor orientations:
+    //      [3 0 1]   [-1  1 -1]   [- 2 -]
+    //      [3 1 4]   [ 2  3  0]   [2 0 1]
+    //      [4 1 2]   [-1 -1  1]   [- - 0]
+    //      [5 3 4]   [ 1 -1 -1]   [1 - -]
+    //
+    // The shape is one large triangle, split into four smaller ones.
+
+    public class OtriTest
+    {
+        // The vertices of the mesh.
+        Vertex[] vertices;
+
+        private Triangle[] CreateExampleMesh()
+        {
+            var triangles = new Triangle[4];
+
+            // Outer space triangle.
+            var dummy = new Triangle() { id = -1 };
+
+            // Setup triangles. Keep in mind the ordering:
+            //
+            // The CreateTriangle method takes vertex arguments in range org-dest-apex,
+            // but internally the vertices get stored in an array with ordering
+            //
+            //    [0] = apex
+            //    [1] = org
+            //    [2] = dest
+            //
+            // This is because, for example, and oriented triange will return as its
+            // origin (Org() method) the element at index [(orientation + 1) % 3].
+            var t0 = triangles[0] = CreateTriangle(0, vertices[0], vertices[1], vertices[3]);
+            var t1 = triangles[1] = CreateTriangle(1, vertices[1], vertices[4], vertices[3]);
+            var t2 = triangles[2] = CreateTriangle(2, vertices[1], vertices[2], vertices[4]);
+            var t3 = triangles[3] = CreateTriangle(3, vertices[3], vertices[4], vertices[5]);
+
+            // Setup connectivity of triangle 0.
+            t0.neighbors[0].tri = dummy;
+            t0.neighbors[1].tri = t1;
+            t0.neighbors[1].orient = 2;
+            t0.neighbors[2].tri = dummy;
+
+            // Setup connectivity of triangle 1.
+            t1.neighbors[0].tri = t2;
+            t1.neighbors[0].orient = 2;
+            t1.neighbors[1].tri = t3;
+            t1.neighbors[1].orient = 0;
+            t1.neighbors[2].tri = t0;
+            t1.neighbors[2].orient = 1;
+
+            // Setup connectivity of triangle 2.
+            t2.neighbors[0].tri = dummy;
+            t2.neighbors[1].tri = dummy;
+            t2.neighbors[2].tri = t1;
+            t2.neighbors[2].orient = 0;
+
+            // Setup connectivity of triangle 3.
+            t3.neighbors[0].tri = t1;
+            t3.neighbors[0].orient = 1;
+            t3.neighbors[1].tri = dummy;
+            t3.neighbors[2].tri = dummy;
+
+            return triangles;
+        }
+
+        private Triangle CreateTriangle(int id, Vertex org, Vertex dest, Vertex apex)
+        {
+            var t = new Triangle() { id = id, hash = id };
+
+            // Node ordering 'plus 1 mod 3'.
+            t.vertices[0] = apex;
+            t.vertices[1] = org;
+            t.vertices[2] = dest;
+
+            return t;
+        }
+
+        [SetUp]
+        public void Initialize()
+        {
+            vertices = new Vertex[6];
+
+            vertices[0] = new Vertex(-2.0, 0.0) { id = 0 };
+            vertices[1] = new Vertex( 0.0, 0.0) { id = 1 };
+            vertices[2] = new Vertex( 2.0, 0.0) { id = 2 };
+            vertices[3] = new Vertex(-1.0, 1.0) { id = 3 };
+            vertices[4] = new Vertex( 1.0, 1.0) { id = 4 };
+            vertices[5] = new Vertex( 0.0, 2.0) { id = 5 };
+        }
+
+        [Test]
+        public void TestOrg()
+        {
+            Otri t = default;
+
+            t.tri = CreateTriangle(0, vertices[1], vertices[4], vertices[3]);
+
+            t.orient = 0;
+            Assert.AreEqual(1, t.Org().ID);
+
+            t.orient = 1;
+            Assert.AreEqual(4, t.Org().ID);
+
+            t.orient = 2;
+            Assert.AreEqual(3, t.Org().ID);
+        }
+
+        [Test]
+        public void TestDest()
+        {
+            Otri t = default;
+
+            t.tri = CreateTriangle(0, vertices[1], vertices[4], vertices[3]);
+
+            t.orient = 0;
+            Assert.AreEqual(4, t.Dest().ID);
+
+            t.orient = 1;
+            Assert.AreEqual(3, t.Dest().ID);
+
+            t.orient = 2;
+            Assert.AreEqual(1, t.Dest().ID);
+        }
+
+        [Test]
+        public void TestApex()
+        {
+            Otri t = default;
+
+            t.tri = CreateTriangle(0, vertices[1], vertices[4], vertices[3]);
+
+            t.orient = 0;
+            Assert.AreEqual(3, t.Apex().ID);
+
+            t.orient = 1;
+            Assert.AreEqual(1, t.Apex().ID);
+
+            t.orient = 2;
+            Assert.AreEqual(4, t.Apex().ID);
+        }
+
+        [Test]
+        public void TestSym()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+            Otri s = default;
+
+            // The center triangle.
+            t.tri = triangles[1];
+
+            t.orient = 0;
+            t.Sym(ref s);
+            Assert.AreEqual(2, s.tri.ID);
+
+            t.orient = 1;
+            t.Sym(ref s);
+            Assert.AreEqual(3, s.tri.ID);
+
+            t.orient = 2;
+            t.Sym(ref s);
+            Assert.AreEqual(0, s.tri.ID);
+        }
+
+        [Test]
+        public void TestLnext()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // The center triangle.
+            t.tri = triangles[1];
+            t.orient = 0;
+
+            t.Lnext();
+            Assert.AreEqual(4, t.Org().ID);
+
+            t.Lnext();
+            Assert.AreEqual(3, t.Org().ID);
+
+            t.Lnext();
+            Assert.AreEqual(1, t.Org().ID);
+        }
+
+        [Test]
+        public void TestLprev()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // The center triangle.
+            t.tri = triangles[1];
+            t.orient = 0;
+
+            t.Lprev();
+            Assert.AreEqual(3, t.Org().ID);
+
+            t.Lprev();
+            Assert.AreEqual(4, t.Org().ID);
+
+            t.Lprev();
+            Assert.AreEqual(1, t.Org().ID);
+        }
+
+        [Test]
+        public void TestOnext()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // Start with the bottom right triangle.
+            t.tri = triangles[2];
+
+            // Start with edge  1 -> 2.
+            t.orient = 0;
+
+            // Make sure we're on the correct edge.
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(2, t.Dest().ID);
+
+            t.Onext();
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(4, t.Dest().ID);
+            Assert.AreEqual(1, t.tri.ID);
+
+            t.Onext();
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+            Assert.AreEqual(0, t.tri.ID);
+
+            // Out of mesh.
+            t.Onext();
+            Assert.AreEqual(-1, t.tri.ID);
+        }
+
+        [Test]
+        public void TestOprev()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // Start with the bottom left triangle.
+            t.tri = triangles[0];
+
+            // Start with edge  1 -> 3.
+            t.orient = 1;
+
+            // Make sure we're on the correct edge.
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+
+            t.Oprev();
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(4, t.Dest().ID);
+            Assert.AreEqual(1, t.tri.ID);
+
+            t.Oprev();
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(2, t.Dest().ID);
+            Assert.AreEqual(2, t.tri.ID);
+
+            // Out of mesh.
+            t.Oprev();
+            Assert.AreEqual(-1, t.tri.ID);
+        }
+
+        [Test]
+        public void TestDnext()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // Start with the bottom left triangle.
+            t.tri = triangles[0];
+
+            // Start with edge  1 -> 3.
+            t.orient = 1;
+
+            // Make sure we're on the correct edge.
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+
+            t.Dnext();
+            Assert.AreEqual(4, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+            Assert.AreEqual(1, t.tri.ID);
+
+            t.Dnext();
+            Assert.AreEqual(5, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+            Assert.AreEqual(3, t.tri.ID);
+
+            // Out of mesh.
+            t.Dnext();
+            Assert.AreEqual(-1, t.tri.ID);
+        }
+
+        [Test]
+        public void TestDprev()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // Start with the top triangle.
+            t.tri = triangles[3];
+
+            // Start with edge  5 -> 3.
+            t.orient = 2;
+
+            // Make sure we're on the correct edge.
+            Assert.AreEqual(5, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+
+            t.Dprev();
+            Assert.AreEqual(4, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+            Assert.AreEqual(1, t.tri.ID);
+
+            t.Dprev();
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+            Assert.AreEqual(0, t.tri.ID);
+
+            // Out of mesh.
+            t.Dprev();
+            Assert.AreEqual(-1, t.tri.ID);
+        }
+
+        [Test]
+        public void TestRnext()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // Start with the bottom left triangle.
+            t.tri = triangles[0];
+
+            // Start with edge  1 -> 3.
+            t.orient = 1;
+
+            // Make sure we're on the correct edge.
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+
+            t.Rnext();
+            Assert.AreEqual(4, t.Org().ID);
+            Assert.AreEqual(1, t.Dest().ID);
+            Assert.AreEqual(2, t.tri.ID);
+
+            t.Rnext();
+            Assert.AreEqual(3, t.Org().ID);
+            Assert.AreEqual(4, t.Dest().ID);
+            Assert.AreEqual(3, t.tri.ID);
+
+            // Back where we started.
+            t.Rnext();
+            Assert.AreEqual(0, t.tri.ID);
+        }
+
+        [Test]
+        public void TestRprev()
+        {
+            var triangles = CreateExampleMesh();
+
+            Otri t = default;
+
+            // Start with the top triangle.
+            t.tri = triangles[3];
+
+            // Start with edge  3 -> 4.
+            t.orient = 0;
+
+            // Make sure we're on the correct edge.
+            Assert.AreEqual(3, t.Org().ID);
+            Assert.AreEqual(4, t.Dest().ID);
+
+            t.Rprev();
+            Assert.AreEqual(4, t.Org().ID);
+            Assert.AreEqual(1, t.Dest().ID);
+            Assert.AreEqual(2, t.tri.ID);
+
+            t.Rprev();
+            Assert.AreEqual(1, t.Org().ID);
+            Assert.AreEqual(3, t.Dest().ID);
+            Assert.AreEqual(0, t.tri.ID);
+
+            // Back where we started.
+            t.Rprev();
+            Assert.AreEqual(3, t.tri.ID);
+        }
+
+        [Test]
+        public void TestBond()
+        {
+            Otri s = default;
+            Otri t = default;
+
+            Otri tmp = default;
+
+            s.tri = CreateTriangle(0, vertices[0], vertices[1], vertices[3]);
+            t.tri = CreateTriangle(1, vertices[1], vertices[4], vertices[3]);
+
+            s.orient = 1; // Edge  1 -> 3.
+            t.orient = 2; // Edge  3 -> 1.
+
+            // Make sure we're on the correct edges.
+            Assert.AreEqual(1, s.Org().ID);
+            Assert.AreEqual(3, s.Dest().ID);
+            Assert.AreEqual(3, t.Org().ID);
+            Assert.AreEqual(1, t.Dest().ID);
+
+            // Check that the triangles don't have neighbors.
+            s.Sym(ref tmp);
+            //Assert.AreEqual(-1, tmp.tri.ID);
+            Assert.IsNull(tmp.tri);
+            t.Sym(ref tmp);
+            //Assert.AreEqual(-1, tmp.tri.ID);
+            Assert.IsNull(tmp.tri);
+
+            // Bond the two triangles.
+            s.Bond(ref t);
+
+            // Check that neighbors are properly set.
+            s.Sym(ref tmp);
+            Assert.AreEqual(1, tmp.tri.ID);
+            t.Sym(ref tmp);
+            Assert.AreEqual(0, tmp.tri.ID);
+        }
+
+        [Test]
+        public void TestDissolve()
+        {
+            // Outer space triangle.
+            var dummy = new Triangle() { id = -1 };
+
+            var triangles = CreateExampleMesh();
+
+            Otri s = default;
+            Otri t = default;
+
+            Otri tmp = default;
+
+            // The bottom left triangle with edge 1 -> 3.
+            s.tri = triangles[0];
+            s.orient = 1;
+
+            // The center triangle with edge 3 -> 1.
+            t.tri = triangles[1];
+            t.orient = 2;
+
+            // Make sure we're on the correct edges.
+            Assert.AreEqual(1, s.Org().ID);
+            Assert.AreEqual(3, s.Dest().ID);
+            Assert.AreEqual(3, t.Org().ID);
+            Assert.AreEqual(1, t.Dest().ID);
+
+            // Check that neighbors are properly set.
+            s.Sym(ref tmp);
+            Assert.AreEqual(1, tmp.tri.ID);
+            t.Sym(ref tmp);
+            Assert.AreEqual(0, tmp.tri.ID);
+
+            // Now dissolve the bond from one side.
+            s.Dissolve(dummy);
+
+            // Check neighbors.
+            s.Sym(ref tmp);
+            Assert.AreEqual(-1, tmp.tri.ID);
+            t.Sym(ref tmp);
+            Assert.AreEqual(0, tmp.tri.ID);
+
+            // And dissolve the bond from the other side.
+            t.Dissolve(dummy);
+
+            // Check neighbors.
+            s.Sym(ref tmp);
+            Assert.AreEqual(-1, tmp.tri.ID);
+            t.Sym(ref tmp);
+            Assert.AreEqual(-1, tmp.tri.ID);
+        }
+    }
+}
diff --git a/src/Triangle.Tests/Triangle.Tests.csproj b/src/Triangle.Tests/Triangle.Tests.csproj
new file mode 100644
index 0000000..47b78b0
--- /dev/null
+++ b/src/Triangle.Tests/Triangle.Tests.csproj
@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+	<RootNamespace>TriangleNet.Tests</RootNamespace>
+    <AssemblyName>Triangle.Tests</AssemblyName>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+
+  <ItemGroup>
+    <PackageReference Include="nunit" Version="3.13.2" />
+    <PackageReference Include="NUnit3TestAdapter" Version="4.2.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Triangle\Triangle.csproj" />
+  </ItemGroup>
+
+</Project>
\ No newline at end of file
diff --git a/src/Triangle.sln b/src/Triangle.sln
index bddd024..99960ec 100644
--- a/src/Triangle.sln
+++ b/src/Triangle.sln
@@ -9,6 +9,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MeshExplorer", "MeshExplore
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Triangle.Rendering", "Triangle.Rendering\Triangle.Rendering.csproj", "{41022E0E-BD0F-439E-BC3A-AABB1B43471B}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Triangle.Tests", "Triangle.Tests\Triangle.Tests.csproj", "{67CCA496-DCD1-4D43-85D5-0A19A3948774}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -41,6 +43,14 @@ Global
 		{41022E0E-BD0F-439E-BC3A-AABB1B43471B}.Release|Any CPU.Build.0 = Release|Any CPU
 		{41022E0E-BD0F-439E-BC3A-AABB1B43471B}.Release|x64.ActiveCfg = Release|x64
 		{41022E0E-BD0F-439E-BC3A-AABB1B43471B}.Release|x64.Build.0 = Release|x64
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Debug|x64.Build.0 = Debug|Any CPU
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Release|Any CPU.Build.0 = Release|Any CPU
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Release|x64.ActiveCfg = Release|Any CPU
+		{67CCA496-DCD1-4D43-85D5-0A19A3948774}.Release|x64.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE