add MergeWith ArgumentException (file does not exist)

Author: Bertk

src/coverlet.core/Coverage.cs

@@ -311,10 +311,17 @@ public CoverageResult GetCoverageResult()
 
       var coverageResult = new CoverageResult { Identifier = Identifier, Modules = modules, InstrumentedResults = _results, Parameters = _parameters };
 
-      if (!string.IsNullOrEmpty(_parameters.MergeWith) && !string.IsNullOrWhiteSpace(_parameters.MergeWith) && _fileSystem.Exists(_parameters.MergeWith))
+      if (!string.IsNullOrEmpty(_parameters.MergeWith) && !string.IsNullOrWhiteSpace(_parameters.MergeWith))
       {
-        string json = _fileSystem.ReadAllText(_parameters.MergeWith);
-        coverageResult.Merge(JsonSerializer.Deserialize<Modules>(json));
+        if (_fileSystem.Exists(_parameters.MergeWith))
+        {
+          string json = _fileSystem.ReadAllText(_parameters.MergeWith);
+          coverageResult.Merge(JsonSerializer.Deserialize<Modules>(json));
+        } else
+        {
+          //_logger.LogError($"MergeWith - file '{_parameters.MergeWith}' does not exist");
+          throw new ArgumentException($"MergeWith - file '{_parameters.MergeWith}' does not exist");
+        }
       }
 
       return coverageResult;

test/coverlet.core.tests/Coverage/CoverageTests.cs

@@ -92,5 +92,43 @@ public void TestCoverageWithTestAssembly()
 
       directory.Delete(true);
     }
+
+    [Fact]
+    public void TestCoverageWrongMergeWith()
+    {
+      string module = GetType().Assembly.Location;
+      string pdb = Path.Combine(Path.GetDirectoryName(module), Path.GetFileNameWithoutExtension(module) + ".pdb");
+
+      DirectoryInfo directory = Directory.CreateDirectory(Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString()));
+
+      File.Copy(module, Path.Combine(directory.FullName, Path.GetFileName(module)), true);
+      File.Copy(pdb, Path.Combine(directory.FullName, Path.GetFileName(pdb)), true);
+
+      // TODO: Find a way to mimick hits
+      var instrumentationHelper =
+          new InstrumentationHelper(new ProcessExitHandler(), new RetryHelper(), new FileSystem(), new Mock<ILogger>().Object,
+                                    new SourceRootTranslator(module, new Mock<ILogger>().Object, new FileSystem(), new AssemblyAdapter()));
+
+      var parameters = new CoverageParameters
+      {
+        IncludeFilters = new string[] { "[coverlet.tests.projectsample.excludedbyattribute*]*" },
+        IncludeDirectories = Array.Empty<string>(),
+        ExcludeFilters = Array.Empty<string>(),
+        ExcludedSourceFiles = Array.Empty<string>(),
+        ExcludeAttributes = Array.Empty<string>(),
+        IncludeTestAssembly = false,
+        SingleHit = false,
+        MergeWith = "blabla",
+        UseSourceLink = false
+      };
+
+      var coverage = new Coverage(Path.Combine(directory.FullName, Path.GetFileName(module)), parameters, _mockLogger.Object, instrumentationHelper, new FileSystem(), new SourceRootTranslator(_mockLogger.Object, new FileSystem()), new CecilSymbolHelper());
+      coverage.PrepareModules();
+
+      ArgumentException exception = Assert.Throws<ArgumentException>(() => coverage.GetCoverageResult());
+      Assert.Contains("blabla", exception.Message);
+
+      directory.Delete(true);
+    }
   }
 }