Add tests; modify readme

Author: ido-namely

README.md

@@ -87,7 +87,7 @@ You can ignore a method or an entire class from code coverage by creating and ap
 Coverlet just uses the type name, so the attributes can be created under any namespace of your choosing.
 
 #### File Path  
-You can also ignore code coverage by specifing files using the `Exclude` property
+You can also ignore specific source files from code coverage using the `Exclude` property
  - Use single or multiple paths (separate by comma)
  - Use absolute or relative paths (relative to the project directory)
  - Use file path or directory path with globbing (e.g `dir1/*.cs`)

test/coverlet.core.tests/Helpers/InstrumentationHelperTests.cs

@@ -2,12 +2,13 @@
 using System.IO;
 
 using Xunit;
-using Coverlet.Core.Helpers;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace Coverlet.Core.Helpers.Tests
 {
     public class InstrumentationHelperTests
-    {
+    {            
         [Fact]
         public void TestGetDependencies()
         {
@@ -79,5 +80,63 @@ public void TestDeleteHitsFile()
             InstrumentationHelper.DeleteHitsFile(tempFile);
             Assert.False(File.Exists(tempFile));
         }
+        
+        
+        public static IEnumerable<object[]> GetExcludedFilesReturnsEmptyArgs => 
+        new[] 
+        {
+            new object[]{null},
+            new object[]{new List<string>()},
+            new object[]{new List<string>(){ Path.GetRandomFileName() }},
+            new object[]{new List<string>(){Path.GetRandomFileName(), 
+                Path.Combine(Directory.GetCurrentDirectory(), Path.GetRandomFileName())}
+            }
+        };
+        
+        [Theory]
+        [MemberData(nameof(GetExcludedFilesReturnsEmptyArgs))]
+        public void TestGetExcludedFilesReturnsEmpty(IEnumerable<string> excludedFiles) 
+        {
+            Assert.False(InstrumentationHelper.GetExcludedFiles(excludedFiles)?.Any());
+        }
+        
+        [Fact]
+        public void TestGetExcludedFilesUsingAbsFile() 
+        {
+            var file = Path.GetRandomFileName();
+            File.Create(file).Dispose();
+            var excludeFiles = InstrumentationHelper.GetExcludedFiles(
+                new List<string>() {Path.Combine(Directory.GetCurrentDirectory(), file)}
+            );
+            File.Delete(file);
+            Assert.Single(excludeFiles);
+        }
+            
+        [Fact]
+        public void TestGetExcludedFilesUsingGlobbing() 
+        {
+            var fileExtension = Path.GetRandomFileName();
+            var paths = new string[]{
+                $"{Path.GetRandomFileName()}.{fileExtension}",
+                $"{Path.GetRandomFileName()}.{fileExtension}"
+            };
+            
+            foreach (var path in paths)
+            {
+                File.Create(path).Dispose();
+            }
+            
+            var excludeFiles = InstrumentationHelper.GetExcludedFiles(
+                new List<string>(){$"*.{fileExtension}"});
+            
+            foreach (var path in paths)
+            {   
+                File.Delete(path);
+            }
+            
+            Assert.Equal(paths.Length, excludeFiles.Count());
+        }
     }
-}
+}
+
+