Test for .Open() if file path is invalid.

OSCADSharp/OSCADSharp.UnitTests/SettingsTests.cs

@@ -30,5 +30,21 @@ namespace OSCADSharp.UnitTests
 
             Assert.AreEqual("", output[1]);
         }
+
+        [TestMethod]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public void Settings_NullOpenSCADPathThrowsError()
+        {
+            Settings.OpenSCADPath = null;
+
+            var cube = new Cube();
+
+            var mock = new Mock<IFileWriter>();
+            mock.Setup(_wrtr => _wrtr.WriteAllLines(It.IsAny<string>(), It.IsAny<string[]>()))
+                .Callback<string, string[]>((path, contents) => { });
+            Dependencies.FileWriter = mock.Object;
+
+            cube.ToFile("test").Open();
+        }
     }
 }

OSCADSharp/OSCADSharp/Files/DefaultFileInvoker.cs

@@ -17,12 +17,26 @@ namespace OSCADSharp.Files
 
         public void CreateModel(string outputFile)
         {
-            Process.Start(Settings.OpenSCADPath, String.Format("-o {0} {1}", outputFile, this.filePath));
+            try
+            {
+                Process.Start(Settings.OpenSCADPath, String.Format("-o {0} {1}", outputFile, this.filePath));
+            }
+            catch (InvalidOperationException)
+            {
+                throw new InvalidOperationException("Cannot open because Settings.OpenSCADPath is not a valid file path.  Please check that the path defined points to you OpenSCAD executable.");
+            }
         }        
 
         public void Open()
         {
-            Process.Start(Settings.OpenSCADPath, String.Format("{0}", this.filePath));
+            try
+            {
+                Process.Start(Settings.OpenSCADPath, String.Format("{0}", this.filePath));
+            }
+            catch (InvalidOperationException)
+            {
+                throw new InvalidOperationException("Cannot open because Settings.OpenSCADPath is not a valid file path.  Please check that the path defined points to you OpenSCAD executable.");
+            }
         }
     }
 }