Fix pdb file locking during instrumentation (#656)

Fix pdb file locking during instrumentation

Author: MarcoRossignoli

Documentation/Changelog.md

@@ -19,6 +19,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 -Fix ConfigureAwait state machine generated branches [#634](https://github.com/tonerdo/coverlet/pull/634)  
 -Fix coverage overwritten if the project has multiple target frameworks [#636](https://github.com/tonerdo/coverlet/issues/177)  
 -Fix cobertura Jenkins reporter + source link support [#614](https://github.com/tonerdo/coverlet/pull/614) by https://github.com/daveMueller  
+-Fix pdb file locking during instrumentation [#656](https://github.com/tonerdo/coverlet/pull/656)
+
 
 ### Improvements
 

src/coverlet.core/Helpers/FileSystem.cs

@@ -21,7 +21,8 @@ public string ReadAllText(string path)
             return File.ReadAllText(path);
         }
 
-        public Stream OpenRead(string path)
+        // We need to partial mock this method on tests
+        public virtual Stream OpenRead(string path)
         {
             return File.OpenRead(path);
         }

src/coverlet.core/Helpers/InstrumentationHelper.cs

@@ -144,7 +144,7 @@ public bool PortablePdbHasLocalSource(string module, out string firstNotFoundDoc
                     if (entry.Type == DebugDirectoryEntryType.CodeView)
                     {
                         var codeViewData = peReader.ReadCodeViewDebugDirectoryData(entry);
-                        using Stream pdbStream = _fileSystem.NewFileStream(codeViewData.Path, FileMode.Open);
+                        using Stream pdbStream = _fileSystem.OpenRead(codeViewData.Path);
                         using MetadataReaderProvider metadataReaderProvider = MetadataReaderProvider.FromPortablePdbStream(pdbStream);
                         MetadataReader metadataReader = null;
                         try

test/coverlet.core.tests/Instrumentation/InstrumenterTests.cs

@@ -374,15 +374,15 @@ public void SkipPpdbWithoutLocalSource()
             {
                 Mock<FileSystem> partialMockFileSystem = new Mock<FileSystem>();
                 partialMockFileSystem.CallBase = true;
-                partialMockFileSystem.Setup(fs => fs.NewFileStream(It.IsAny<string>(), It.IsAny<FileMode>())).Returns((string path, FileMode mode) =>
+                partialMockFileSystem.Setup(fs => fs.OpenRead(It.IsAny<string>())).Returns((string path) =>
                 {
                     if (Path.GetFileName(path) == pdbFileName)
                     {
-                        return new FileStream(Path.Combine(Path.Combine(Directory.GetCurrentDirectory(), "TestAssets"), pdbFileName), mode);
+                        return File.OpenRead(Path.Combine(Path.Combine(Directory.GetCurrentDirectory(), "TestAssets"), pdbFileName));
                     }
                     else
                     {
-                        return new FileStream(path, mode);
+                        return File.OpenRead(path);
                     }
                 });
                 partialMockFileSystem.Setup(fs => fs.Exists(It.IsAny<string>())).Returns((string path) =>