Add unit tests for SelfDiagnosticsModule (#1706)

* Add unit tests for SelfDiagnosticsModule

* Add a line for debugging in case the test fails

* Clean up config file after use in each unit test case.

Co-authored-by: Cijo Thomas <cithomas@microsoft.com>

test/OpenTelemetry.Tests/Internal/SelfDiagnosticsConfigRefresherTest.cs

@@ -18,43 +18,97 @@
 using System.IO;
 using System.Text;
 using Xunit;
+using Xunit.Abstractions;
 
 namespace OpenTelemetry.Internal.Tests
 {
     public class SelfDiagnosticsConfigRefresherTest
     {
         private static readonly string ConfigFilePath = SelfDiagnosticsConfigParser.ConfigFileName;
         private static readonly byte[] MessageOnNewFile = SelfDiagnosticsConfigRefresher.MessageOnNewFile;
+        private static readonly string MessageOnNewFileString = Encoding.UTF8.GetString(SelfDiagnosticsConfigRefresher.MessageOnNewFile);
+
+        private readonly ITestOutputHelper output;
+
+        public SelfDiagnosticsConfigRefresherTest(ITestOutputHelper output)
+        {
+            this.output = output;
+        }
+
+        [Fact]
+        [Trait("Platform", "Any")]
+        public void SelfDiagnosticsConfigRefresher_OmitAsConfigured()
+        {
+            try
+            {
+                CreateConfigFile();
+                using var configRefresher = new SelfDiagnosticsConfigRefresher();
+
+                // Emitting event of EventLevel.Warning
+                OpenTelemetrySdkEventSource.Log.SpanProcessorQueueIsExhausted();
+
+                int bufferSize = 512;
+                byte[] actualBytes = ReadFile(bufferSize);
+                string logText = Encoding.UTF8.GetString(actualBytes);
+                this.output.WriteLine(logText);  // for debugging in case the test fails
+                Assert.StartsWith(MessageOnNewFileString, logText);
+
+                // The event was omitted
+                Assert.Equal('\0', (char)actualBytes[MessageOnNewFile.Length]);
+            }
+            finally
+            {
+                CleanupConfigFile();
+            }
+        }
 
         [Fact]
         [Trait("Platform", "Any")]
-        public void SelfDiagnosticsConfigRefresher_FileShare()
+        public void SelfDiagnosticsConfigRefresher_CaptureAsConfigured()
         {
             try
             {
                 CreateConfigFile();
                 using var configRefresher = new SelfDiagnosticsConfigRefresher();
 
-                var outputFileName = Path.GetFileName(Process.GetCurrentProcess().MainModule.FileName) + "."
-                        + Process.GetCurrentProcess().Id + ".log";
-                var outputFilePath = Path.Combine(".", outputFileName);
-                using var file = File.Open(outputFilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
-                byte[] actualBytes = new byte[MessageOnNewFile.Length];
-                file.Read(actualBytes, 0, actualBytes.Length);
-                Assert.Equal(MessageOnNewFile, actualBytes);
+                // Emitting event of EventLevel.Error
+                OpenTelemetrySdkEventSource.Log.SpanProcessorException("Event string sample", "Exception string sample");
+
+                int bufferSize = 512;
+                byte[] actualBytes = ReadFile(bufferSize);
+                string logText = Encoding.UTF8.GetString(actualBytes);
+                Assert.StartsWith(MessageOnNewFileString, logText);
+
+                // The event was captured
+                string logLine = logText.Substring(MessageOnNewFileString.Length);
+                string logMessage = ParseLogMessage(logLine);
+                string expectedMessage = "Unknown error in SpanProcessor event '{0}': '{1}'.{Event string sample}{Exception string sample}";
+                Assert.StartsWith(expectedMessage, logMessage);
             }
             finally
             {
-                try
-                {
-                    File.Delete(ConfigFilePath);
-                }
-                catch
-                {
-                }
+                CleanupConfigFile();
             }
         }
 
+        private static string ParseLogMessage(string logLine)
+        {
+            int timestampPrefixLength = "2020-08-14T20:33:24.4788109Z:".Length;
+            Assert.Matches(@"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{7}Z:", logLine.Substring(0, timestampPrefixLength));
+            return logLine.Substring(timestampPrefixLength);
+        }
+
+        private static byte[] ReadFile(int byteCount)
+        {
+            var outputFileName = Path.GetFileName(Process.GetCurrentProcess().MainModule.FileName) + "."
+                    + Process.GetCurrentProcess().Id + ".log";
+            var outputFilePath = Path.Combine(".", outputFileName);
+            using var file = File.Open(outputFilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
+            byte[] actualBytes = new byte[byteCount];
+            file.Read(actualBytes, 0, byteCount);
+            return actualBytes;
+        }
+
         private static void CreateConfigFile()
         {
             string configJson = @"{
@@ -66,5 +120,16 @@ private static void CreateConfigFile()
             byte[] configBytes = Encoding.UTF8.GetBytes(configJson);
             file.Write(configBytes, 0, configBytes.Length);
         }
+
+        private static void CleanupConfigFile()
+        {
+            try
+            {
+                File.Delete(ConfigFilePath);
+            }
+            catch
+            {
+            }
+        }
     }
 }