Probably due to the code changes in e813ebcc03 (additional use of Microsoft.CodeAnalysis.CSharp),

the stupid build system started copying an older version of System.Collections.Immutable and System.ValueType (the one referenced by Roslyn) to the BamlDecompiler.Tests output directly, causing the tests to fail due to a missing dependency.

Upgrade our Roslyn package version and downgrade the System.Collections.Immutable and System.ValueType versions, so that there's only one version of each assembly in play.

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -32,8 +32,8 @@
 
   <ItemGroup>
     <PackageReference Include="DiffLib" Version="1.0.0.55" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="2.3.2" />
-    <PackageReference Include="System.Collections.Immutable" Version="1.4.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="2.4.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="1.3.1" />
     <PackageReference Include="NUnit" Version="2.6.3" />
     <PackageReference Include="NUnitTestAdapter" Version="2.0.0" />
   </ItemGroup>

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -51,8 +51,8 @@
   <ItemGroup>
     <PackageReference Include="Humanizer.Core" Version="2.2.0" />
     <PackageReference Include="Newtonsoft.Json" Version="10.0.3" />
-    <PackageReference Include="System.Collections.Immutable" Version="1.4.0" />
-    <PackageReference Include="System.ValueTuple" Version="4.4.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="1.3.1" />
+    <PackageReference Include="System.ValueTuple" Version="4.3.0" />
   </ItemGroup>
 
   <ItemGroup>