Fix tests that used Program

Needed to substitute for Program a bit better.

Author: jcansdale

test/GitHub.Api.UnitTests/SimpleApiClientFactoryTests.cs

@@ -16,7 +16,7 @@ public class TheCreateMethod
         public async Task CreatesNewInstanceOfSimpleApiClient()
         {
             const string url = "https://github.com/github/CreatesNewInstanceOfSimpleApiClient";
-            var program = Substitute.For<IProgram>();
+            var program = CreateProgram();
             var keychain = Substitute.For<IKeychain>();
             var enterpriseProbe = Substitute.For<IEnterpriseProbe>();
             var wikiProbe = Substitute.For<IWikiProbe>();
@@ -40,7 +40,7 @@ public class TheClearFromCacheMethod
         public async Task RemovesClientFromCache()
         {
             const string url = "https://github.com/github/RemovesClientFromCache";
-            var program = Substitute.For<IProgram>();
+            var program = CreateProgram();
             var enterpriseProbe = Substitute.For<IEnterpriseProbe>();
             var wikiProbe = Substitute.For<IWikiProbe>();
             var factory = new SimpleApiClientFactory(
@@ -56,6 +56,13 @@ public async Task RemovesClientFromCache()
         }
     }
 
+    static IProgram CreateProgram()
+    {
+        var program = Substitute.For<IProgram>();
+        program.ProductHeader.Returns(new ProductHeaderValue("ProductName"));
+        return program;
+    }
+
     static IKeychain CreateKeychain()
     {
         var result = Substitute.For<IKeychain>();