diff --git a/test/DemaConsulting.SpdxTool.Tests/DiagramTests.cs b/test/DemaConsulting.SpdxTool.Tests/DiagramTests.cs
new file mode 100644
index 0000000..be13533
--- /dev/null
+++ b/test/DemaConsulting.SpdxTool.Tests/DiagramTests.cs
@@ -0,0 +1,309 @@
+// Copyright (c) 2024 DEMA Consulting
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+namespace DemaConsulting.SpdxTool.Tests;
+
+/// <summary>
+///     Tests for the 'diagram' command
+/// </summary>
+[TestClass]
+public class DiagramTests
+{
+    /// <summary>
+    ///     Test the 'diagram' command with missing arguments
+    /// </summary>
+    [TestMethod]
+    public void DiagramCommand_MissingArguments()
+    {
+        // Act: Run the command
+        var exitCode = Runner.Run(
+            out var output,
+            "dotnet",
+            "DemaConsulting.SpdxTool.dll",
+            "diagram");
+
+        // Assert: Verify error reported
+        Assert.AreEqual(1, exitCode);
+        Assert.Contains("'diagram' command invalid arguments", output);
+    }
+
+    /// <summary>
+    ///     Test the 'diagram' command with insufficient arguments
+    /// </summary>
+    [TestMethod]
+    public void DiagramCommand_InsufficientArguments()
+    {
+        // Act: Run the command
+        var exitCode = Runner.Run(
+            out var output,
+            "dotnet",
+            "DemaConsulting.SpdxTool.dll",
+            "diagram",
+            "test.spdx.json");
+
+        // Assert: Verify error reported
+        Assert.AreEqual(1, exitCode);
+        Assert.Contains("'diagram' command invalid arguments", output);
+    }
+
+    /// <summary>
+    ///     Test the 'diagram' command with missing SPDX file
+    /// </summary>
+    [TestMethod]
+    public void DiagramCommand_MissingSpdxFile()
+    {
+        // Act: Run the command
+        var exitCode = Runner.Run(
+            out var output,
+            "dotnet",
+            "DemaConsulting.SpdxTool.dll",
+            "diagram",
+            "missing.spdx.json",
+            "output.mermaid.txt");
+
+        // Assert: Verify error reported
+        Assert.AreEqual(1, exitCode);
+        Assert.Contains("File not found: missing.spdx.json", output);
+    }
+
+    /// <summary>
+    ///     Test the 'diagram' command with invalid option
+    /// </summary>
+    [TestMethod]
+    public void DiagramCommand_InvalidOption()
+    {
+        const string spdxContents =
+            """
+            {
+              "files": [],
+              "packages": [],
+              "relationships": [],
+              "spdxVersion": "SPDX-2.2",
+              "dataLicense": "CC0-1.0",
+              "SPDXID": "SPDXRef-DOCUMENT",
+              "name": "Test Document",
+              "documentNamespace": "https://sbom.spdx.org",
+              "creationInfo": {
+                "created": "2021-10-01T00:00:00Z",
+                "creators": [ "Person: Malcolm Nixon" ]
+              }
+            }
+            """;
+
+        try
+        {
+            // Arrange: Write the SPDX file
+            File.WriteAllText("test.spdx.json", spdxContents);
+
+            // Act: Run the command
+            var exitCode = Runner.Run(
+                out var output,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "diagram",
+                "test.spdx.json",
+                "output.mermaid.txt",
+                "invalid-option");
+
+            // Assert: Verify error reported
+            Assert.AreEqual(1, exitCode);
+            Assert.Contains("'diagram' command invalid option invalid-option", output);
+        }
+        finally
+        {
+            File.Delete("test.spdx.json");
+        }
+    }
+
+    /// <summary>
+    ///     Test the 'diagram' command to generate a diagram
+    /// </summary>
+    [TestMethod]
+    public void DiagramCommand_GenerateDiagram()
+    {
+        const string spdxContents =
+            """
+            {
+              "files": [],
+              "packages": [
+                {
+                  "SPDXID": "SPDXRef-Application",
+                  "name": "Test Application",
+                  "versionInfo": "1.2.3",
+                  "downloadLocation": "https://github.com/demaconsulting/SpdxTool",
+                  "licenseConcluded": "MIT"
+                },
+                {
+                  "SPDXID": "SPDXRef-Library",
+                  "name": "Test Library",
+                  "versionInfo": "2.3.4",
+                  "downloadLocation": "https://github.com/demaconsulting/SpdxTool",
+                  "licenseConcluded": "MIT"
+                }
+              ],
+              "relationships": [
+                {
+                  "spdxElementId": "SPDXRef-DOCUMENT",
+                  "relatedSpdxElement": "SPDXRef-Application",
+                  "relationshipType": "DESCRIBES"
+                },
+                {
+                  "spdxElementId": "SPDXRef-Application",
+                  "relatedSpdxElement": "SPDXRef-Library",
+                  "relationshipType": "DEPENDS_ON"
+                }
+              ],
+              "spdxVersion": "SPDX-2.2",
+              "dataLicense": "CC0-1.0",
+              "SPDXID": "SPDXRef-DOCUMENT",
+              "name": "Test Document",
+              "documentNamespace": "https://sbom.spdx.org",
+              "creationInfo": {
+                "created": "2021-10-01T00:00:00Z",
+                "creators": [ "Person: Malcolm Nixon" ]
+              }
+            }
+            """;
+
+        try
+        {
+            // Arrange: Write the SPDX file
+            File.WriteAllText("test.spdx.json", spdxContents);
+
+            // Act: Run the command
+            var exitCode = Runner.Run(
+                out _,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "diagram",
+                "test.spdx.json",
+                "test.mermaid.txt");
+
+            // Assert: Verify success reported
+            Assert.AreEqual(0, exitCode);
+
+            // Assert: Verify the mermaid file was created
+            Assert.IsTrue(File.Exists("test.mermaid.txt"));
+            var mermaid = File.ReadAllText("test.mermaid.txt");
+            Assert.Contains("erDiagram", mermaid);
+            Assert.Contains("Test Application / 1.2.3", mermaid);
+            Assert.Contains("Test Library / 2.3.4", mermaid);
+            Assert.Contains("DEPENDS_ON", mermaid);
+        }
+        finally
+        {
+            File.Delete("test.spdx.json");
+            File.Delete("test.mermaid.txt");
+        }
+    }
+
+    /// <summary>
+    ///     Test the 'diagram' command with tools option
+    /// </summary>
+    [TestMethod]
+    public void DiagramCommand_WithTools()
+    {
+        const string spdxContents =
+            """
+            {
+              "files": [],
+              "packages": [
+                {
+                  "SPDXID": "SPDXRef-Application",
+                  "name": "Test Application",
+                  "versionInfo": "1.2.3",
+                  "downloadLocation": "https://github.com/demaconsulting/SpdxTool",
+                  "licenseConcluded": "MIT"
+                },
+                {
+                  "SPDXID": "SPDXRef-Tool",
+                  "name": "Build Tool",
+                  "versionInfo": "3.4.5",
+                  "downloadLocation": "https://github.com/demaconsulting/SpdxTool",
+                  "licenseConcluded": "MIT"
+                }
+              ],
+              "relationships": [
+                {
+                  "spdxElementId": "SPDXRef-DOCUMENT",
+                  "relatedSpdxElement": "SPDXRef-Application",
+                  "relationshipType": "DESCRIBES"
+                },
+                {
+                  "spdxElementId": "SPDXRef-Tool",
+                  "relatedSpdxElement": "SPDXRef-Application",
+                  "relationshipType": "BUILD_TOOL_OF"
+                }
+              ],
+              "spdxVersion": "SPDX-2.2",
+              "dataLicense": "CC0-1.0",
+              "SPDXID": "SPDXRef-DOCUMENT",
+              "name": "Test Document",
+              "documentNamespace": "https://sbom.spdx.org",
+              "creationInfo": {
+                "created": "2021-10-01T00:00:00Z",
+                "creators": [ "Person: Malcolm Nixon" ]
+              }
+            }
+            """;
+
+        try
+        {
+            // Arrange: Write the SPDX file
+            File.WriteAllText("test.spdx.json", spdxContents);
+
+            // Act: Run the command without tools option
+            var exitCode = Runner.Run(
+                out _,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "diagram",
+                "test.spdx.json",
+                "test-no-tools.mermaid.txt");
+
+            // Assert: Verify success and tools not included
+            Assert.AreEqual(0, exitCode);
+            var mermaidNoTools = File.ReadAllText("test-no-tools.mermaid.txt");
+            Assert.DoesNotContain("Build Tool", mermaidNoTools);
+
+            // Act: Run the command with tools option
+            exitCode = Runner.Run(
+                out _,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "diagram",
+                "test.spdx.json",
+                "test-with-tools.mermaid.txt",
+                "tools");
+
+            // Assert: Verify success and tools included
+            Assert.AreEqual(0, exitCode);
+            var mermaidWithTools = File.ReadAllText("test-with-tools.mermaid.txt");
+            Assert.Contains("Build Tool / 3.4.5", mermaidWithTools);
+            Assert.Contains("BUILD_TOOL_OF", mermaidWithTools);
+        }
+        finally
+        {
+            File.Delete("test.spdx.json");
+            File.Delete("test-no-tools.mermaid.txt");
+            File.Delete("test-with-tools.mermaid.txt");
+        }
+    }
+}
diff --git a/test/DemaConsulting.SpdxTool.Tests/ValidateTests.cs b/test/DemaConsulting.SpdxTool.Tests/ValidateTests.cs
new file mode 100644
index 0000000..298fd4e
--- /dev/null
+++ b/test/DemaConsulting.SpdxTool.Tests/ValidateTests.cs
@@ -0,0 +1,313 @@
+// Copyright (c) 2024 DEMA Consulting
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+namespace DemaConsulting.SpdxTool.Tests;
+
+/// <summary>
+///     Tests for the 'validate' command
+/// </summary>
+[TestClass]
+public class ValidateTests
+{
+    /// <summary>
+    ///     Test the 'validate' command with missing arguments
+    /// </summary>
+    [TestMethod]
+    public void ValidateCommand_MissingArguments()
+    {
+        // Act: Run the command
+        var exitCode = Runner.Run(
+            out var output,
+            "dotnet",
+            "DemaConsulting.SpdxTool.dll",
+            "validate");
+
+        // Assert: Verify error reported
+        Assert.AreEqual(1, exitCode);
+        Assert.Contains("'validate' command missing arguments", output);
+    }
+
+    /// <summary>
+    ///     Test the 'validate' command with missing SPDX file
+    /// </summary>
+    [TestMethod]
+    public void ValidateCommand_MissingSpdxFile()
+    {
+        // Act: Run the command
+        var exitCode = Runner.Run(
+            out var output,
+            "dotnet",
+            "DemaConsulting.SpdxTool.dll",
+            "validate",
+            "missing.spdx.json");
+
+        // Assert: Verify error reported
+        Assert.AreEqual(1, exitCode);
+        Assert.Contains("File not found: missing.spdx.json", output);
+    }
+
+    /// <summary>
+    ///     Test the 'validate' command with a valid SPDX document
+    /// </summary>
+    [TestMethod]
+    public void ValidateCommand_ValidDocument()
+    {
+        const string spdxContents =
+            """
+            {
+              "files": [],
+              "packages": [
+                {
+                  "SPDXID": "SPDXRef-Package",
+                  "name": "Test Package",
+                  "versionInfo": "1.0.0",
+                  "downloadLocation": "https://github.com/demaconsulting/SpdxTool",
+                  "filesAnalyzed": false,
+                  "licenseConcluded": "MIT"
+                }
+              ],
+              "relationships": [
+                {
+                  "spdxElementId": "SPDXRef-DOCUMENT",
+                  "relatedSpdxElement": "SPDXRef-Package",
+                  "relationshipType": "DESCRIBES"
+                }
+              ],
+              "spdxVersion": "SPDX-2.2",
+              "dataLicense": "CC0-1.0",
+              "SPDXID": "SPDXRef-DOCUMENT",
+              "name": "Test Document",
+              "documentNamespace": "https://sbom.spdx.org",
+              "creationInfo": {
+                "created": "2021-10-01T00:00:00Z",
+                "creators": [ "Person: Malcolm Nixon" ]
+              }
+            }
+            """;
+
+        try
+        {
+            // Arrange: Write the SPDX file
+            File.WriteAllText("test.spdx.json", spdxContents);
+
+            // Act: Run the command
+            var exitCode = Runner.Run(
+                out _,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "validate",
+                "test.spdx.json");
+
+            // Assert: Verify success reported
+            Assert.AreEqual(0, exitCode);
+        }
+        finally
+        {
+            File.Delete("test.spdx.json");
+        }
+    }
+
+    /// <summary>
+    ///     Test the 'validate' command with valid document without files analyzed
+    /// </summary>
+    [TestMethod]
+    public void ValidateCommand_NoFilesAnalyzed()
+    {
+        const string spdxContents =
+            """
+            {
+              "files": [],
+              "packages": [
+                {
+                  "SPDXID": "SPDXRef-Package",
+                  "name": "Test Package",
+                  "versionInfo": "1.0.0",
+                  "downloadLocation": "NOASSERTION",
+                  "filesAnalyzed": false,
+                  "licenseConcluded": "NOASSERTION"
+                }
+              ],
+              "relationships": [
+                {
+                  "spdxElementId": "SPDXRef-DOCUMENT",
+                  "relatedSpdxElement": "SPDXRef-Package",
+                  "relationshipType": "DESCRIBES"
+                }
+              ],
+              "spdxVersion": "SPDX-2.2",
+              "dataLicense": "CC0-1.0",
+              "SPDXID": "SPDXRef-DOCUMENT",
+              "name": "Test Document",
+              "documentNamespace": "https://sbom.spdx.org",
+              "creationInfo": {
+                "created": "2021-10-01T00:00:00Z",
+                "creators": [ "Person: Malcolm Nixon" ]
+              }
+            }
+            """;
+
+        try
+        {
+            // Arrange: Write the SPDX file
+            File.WriteAllText("test.spdx.json", spdxContents);
+
+            // Act: Run the command
+            var exitCode = Runner.Run(
+                out _,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "validate",
+                "test.spdx.json");
+
+            // Assert: Verify success (validation checks are lenient)
+            Assert.AreEqual(0, exitCode);
+        }
+        finally
+        {
+            File.Delete("test.spdx.json");
+        }
+    }
+
+    /// <summary>
+    ///     Test the 'validate' command with NTIA option on valid document
+    /// </summary>
+    [TestMethod]
+    public void ValidateCommand_NtiaValid()
+    {
+        const string spdxContents =
+            """
+            {
+              "files": [],
+              "packages": [
+                {
+                  "SPDXID": "SPDXRef-Package",
+                  "name": "Test Package",
+                  "versionInfo": "1.0.0",
+                  "supplier": "Organization: Test",
+                  "downloadLocation": "https://github.com/demaconsulting/SpdxTool",
+                  "filesAnalyzed": false,
+                  "licenseConcluded": "MIT"
+                }
+              ],
+              "relationships": [
+                {
+                  "spdxElementId": "SPDXRef-DOCUMENT",
+                  "relatedSpdxElement": "SPDXRef-Package",
+                  "relationshipType": "DESCRIBES"
+                }
+              ],
+              "spdxVersion": "SPDX-2.2",
+              "dataLicense": "CC0-1.0",
+              "SPDXID": "SPDXRef-DOCUMENT",
+              "name": "Test Document",
+              "documentNamespace": "https://sbom.spdx.org",
+              "creationInfo": {
+                "created": "2021-10-01T00:00:00Z",
+                "creators": [ "Person: Malcolm Nixon" ]
+              }
+            }
+            """;
+
+        try
+        {
+            // Arrange: Write the SPDX file
+            File.WriteAllText("test.spdx.json", spdxContents);
+
+            // Act: Run the command with NTIA flag
+            var exitCode = Runner.Run(
+                out _,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "validate",
+                "test.spdx.json",
+                "ntia");
+
+            // Assert: Verify success reported
+            Assert.AreEqual(0, exitCode);
+        }
+        finally
+        {
+            File.Delete("test.spdx.json");
+        }
+    }
+
+    /// <summary>
+    ///     Test the 'validate' command with NTIA option on invalid document
+    /// </summary>
+    [TestMethod]
+    public void ValidateCommand_NtiaInvalid()
+    {
+        const string spdxContents =
+            """
+            {
+              "files": [],
+              "packages": [
+                {
+                  "SPDXID": "SPDXRef-Package",
+                  "name": "Test Package",
+                  "versionInfo": "1.0.0",
+                  "downloadLocation": "https://github.com/demaconsulting/SpdxTool",
+                  "filesAnalyzed": false,
+                  "licenseConcluded": "MIT"
+                }
+              ],
+              "relationships": [
+                {
+                  "spdxElementId": "SPDXRef-DOCUMENT",
+                  "relatedSpdxElement": "SPDXRef-Package",
+                  "relationshipType": "DESCRIBES"
+                }
+              ],
+              "spdxVersion": "SPDX-2.2",
+              "dataLicense": "CC0-1.0",
+              "SPDXID": "SPDXRef-DOCUMENT",
+              "name": "Test Document",
+              "documentNamespace": "https://sbom.spdx.org",
+              "creationInfo": {
+                "created": "2021-10-01T00:00:00Z",
+                "creators": [ "Person: Malcolm Nixon" ]
+              }
+            }
+            """;
+
+        try
+        {
+            // Arrange: Write the SPDX file
+            File.WriteAllText("test.spdx.json", spdxContents);
+
+            // Act: Run the command with NTIA flag
+            var exitCode = Runner.Run(
+                out var output,
+                "dotnet",
+                "DemaConsulting.SpdxTool.dll",
+                "validate",
+                "test.spdx.json",
+                "ntia");
+
+            // Assert: Verify error reported (missing supplier for NTIA)
+            Assert.AreEqual(1, exitCode);
+            Assert.Contains("Issues in test.spdx.json", output);
+        }
+        finally
+        {
+            File.Delete("test.spdx.json");
+        }
+    }
+}