Added a ThrowIfNotAvailable to ISolutionManager.

Updated BuildIntegratedProjectUtility to handle cases where
solutionDirectory is null or is a relative path

Fixes NuGet/Home#1081

src/PackageManagement/IDE/ISolutionManager.cs

@@ -63,6 +63,8 @@ public interface ISolutionManager
         /// passed in.
         /// </returns>
         NuGetProject GetNuGetProject(string nuGetProjectSafeName);
+
+        void ThrowIfNotAvailable();
     }
 
     public class NuGetProjectEventArgs : EventArgs

src/ProjectManagement/Strings.resx

@@ -234,6 +234,9 @@
   <data name="RemovingPackageFromMSBuildProject" xml:space="preserve">
     <value>Removing package '{0}' from project '{1}'</value>
   </data>
+  <data name="SolutionDirectoryShouldBeANonNullFullPath" xml:space="preserve">
+    <value>Solution directory must be a non-null full path</value>
+  </data>
   <data name="TokenHasNoValue" xml:space="preserve">
     <value>The replacement token '{0}' has no value</value>
   </data>

src/ProjectManagement/Utility/BuildIntegratedProjectUtility.cs

@@ -31,15 +31,22 @@ public static class BuildIntegratedProjectUtility
 
         public static string GetEffectiveGlobalPackagesFolder(string solutionDirectory, ISettings settings)
         {
-            // solutionDirectory could be null or empty. If not, it should be a full path, not a relative path
-            Debug.Assert(string.IsNullOrEmpty(solutionDirectory) || Path.IsPathRooted(solutionDirectory));
+            if (settings == null)
+            {
+                throw new ArgumentNullException(nameof(settings));
+            }
 
             var globalPackagesFolder = SettingsUtility.GetGlobalPackagesFolder(settings);
-            if (string.IsNullOrEmpty(solutionDirectory))
+            if (Path.IsPathRooted(globalPackagesFolder))
             {
                 return globalPackagesFolder;
             }
 
+            if (string.IsNullOrEmpty(solutionDirectory) || !Path.IsPathRooted(solutionDirectory))
+            {
+                throw new ArgumentException(Strings.SolutionDirectoryShouldBeANonNullFullPath);
+            }
+
             return Path.GetFullPath(Path.Combine(solutionDirectory, globalPackagesFolder));
         }
 

test/Test.Utility/TestSolutionManager.cs

@@ -143,6 +143,11 @@ public bool IsSolutionOpen
             get { return NuGetProjects.Count > 0; }
         }
 
+        public void ThrowIfNotAvailable()
+        {
+
+        }
+
         public INuGetProjectContext NuGetProjectContext { get; set; }
 
 #pragma warning disable 0067