Add output compilation verification

Author: 333fred

src/Compilers/CSharp/Test/Semantic/SourceGeneration/GeneratorDriverTests.cs

@@ -2464,7 +2464,7 @@ class C { }
             }));
 
             GeneratorDriver driver = CSharpGeneratorDriver.Create([generator], parseOptions: parseOptions, driverOptions: TestOptions.GeneratorDriverOptions);
-            driver = driver.RunGenerators(compilation);
+            driver = driver.RunGeneratorsAndUpdateCompilation(compilation, out var outputCompilation, out _);
             var runResult = driver.GetRunResult().Results[0];
 
             Assert.Single(runResult.GeneratedSources);
@@ -2480,6 +2480,8 @@ internal sealed partial class EmbeddedAttribute : global::System.Attribute
             }
             """, generatedSource.SourceText.ToString());
             Assert.Equal("Microsoft.CodeAnalysis.EmbeddedAttribute.cs", generatedSource.HintName);
+
+            outputCompilation.VerifyDiagnostics();
         }
 
         [Fact]

src/Compilers/VisualBasic/Test/Semantic/SourceGeneration/GeneratorDriverTests.vb

@@ -646,7 +646,9 @@ End Class
                                                                                          End Sub))
 
             Dim driver As GeneratorDriver = VisualBasicGeneratorDriver.Create(ImmutableArray.Create(Of ISourceGenerator)(generator), parseOptions:=parseOptions, driverOptions:=TestOptions.GeneratorDriverOptions)
-            driver = driver.RunGenerators(compilation)
+            Dim outputCompilation As Compilation = Nothing
+            Dim diagnostics As ImmutableArray(Of Diagnostic) = Nothing
+            driver = driver.RunGeneratorsAndUpdateCompilation(compilation, outputCompilation, diagnostics)
             Dim runResult = driver.GetRunResult().Results(0)
 
             Assert.Single(runResult.GeneratedSources)
@@ -659,6 +661,8 @@ End Class
     End Class
 End Namespace", generatedSource.SourceText.ToString())
             Assert.Equal("Microsoft.CodeAnalysis.EmbeddedAttribute.vb", generatedSource.HintName)
+
+            outputCompilation.VerifyDiagnostics()
         End Sub
 
         <Fact>