test: bring coverage to 94% for RuneExtensions

X10D.Tests/src/Text/RuneTests.cs

@@ -28,7 +28,7 @@ public class RuneTests
     }
 
     [TestMethod]
-    public void RepeatShouldBeCorrect()
+    public void Repeat_ShouldRepeatRune_GivenValidCount()
     {
         const string expected = "aaaaaaaaaa";
         var rune = new Rune('a');
@@ -38,7 +38,7 @@ public class RuneTests
     }
 
     [TestMethod]
-    public void RepeatOneCountShouldBeLength1String()
+    public void Repeat_ShouldReturnStringOfLength1_GivenCountOf1()
     {
         string repeated = new Rune('a').Repeat(1);
         Assert.AreEqual(1, repeated.Length);
@@ -46,7 +46,20 @@ public class RuneTests
     }
 
     [TestMethod]
-    public void RepeatCodepoint_0000_007F_ShouldCorrect()
+    public void Repeat_ShouldThrowArgumentOutOfRangeException_GivenNegativeCount()
+    {
+        var rune = new Rune('a');
+        Assert.ThrowsException<ArgumentOutOfRangeException>(() => rune.Repeat(-1));
+    }
+
+    [TestMethod]
+    public void Repeat_ShouldReturnEmptyString_GivenCountOf0()
+    {
+        Assert.AreEqual(string.Empty, new Rune('a').Repeat(0));
+    }
+
+    [TestMethod]
+    public void RepeatCodepoint_0000_007F_ShouldReturnString()
     {
         string repeated = new Rune(69).Repeat(16);
         Assert.AreEqual(16, repeated.Length);
@@ -54,7 +67,7 @@ public class RuneTests
     }
 
     [TestMethod]
-    public void RepeatCodepoint_0080_07FF_ShouldCorrect()
+    public void RepeatCodepoint_0080_07FF_ShouldReturnString()
     {
         string repeated = new Rune(192).Repeat(8);
         Assert.AreEqual(8, repeated.Length);
@@ -62,7 +75,7 @@ public class RuneTests
     }
 
     [TestMethod]
-    public void RepeatCodepoint_0800_FFFF_ShouldCorrect()
+    public void RepeatCodepoint_0800_FFFF_ShouldReturnString()
     {
         string repeated = new Rune(0x0800).Repeat(5);
         Assert.AreEqual(5, repeated.Length);
@@ -70,23 +83,11 @@ public class RuneTests
     }
 
     [TestMethod]
-    public void RepeatCodepointBeyondU10000ShouldCorrect()
+    public void RepeatCodepointBeyondU10000ShouldReturnString()
     {
         string repeated = new Rune('\uD800', '\uDC00').Repeat(6);
         Assert.AreEqual(12, repeated.Length);
         Assert.AreEqual("𐀀𐀀𐀀𐀀𐀀𐀀", repeated);
     }
-
-    [TestMethod]
-    public void RepeatZeroCountShouldBeEmpty()
-    {
-        Assert.AreEqual(string.Empty, new Rune('a').Repeat(0));
-    }
-
-    [TestMethod]
-    public void RepeatNegativeCountShouldThrow()
-    {
-        Assert.ThrowsException<ArgumentOutOfRangeException>(() => new Rune('a').Repeat(-1));
-    }
 }
 #endif

X10D/src/Text/RuneExtensions.cs

@@ -1,5 +1,6 @@
 #if NETCOREAPP3_0_OR_GREATER
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Contracts;
 using System.Globalization;
 using System.Runtime.CompilerServices;
@@ -82,7 +83,7 @@ public static class RuneExtensions
             // Codepoint 0x10000 and beyond will takes **only** 2 UTF-16 character.
             case 4:
                 {
-                    return string.Create(count * 2, value, (span, rune) =>
+                    return string.Create(count * 2, value, (span, _) =>
                     {
                         unsafe
                         {
@@ -98,12 +99,21 @@ public static class RuneExtensions
                 }
 
             default:
-                var msg = string.Format(CultureInfo.CurrentCulture, ExceptionMessages.UnexpectedRuneUtf8SequenceLength, length);
+                return Default();
+        }
+
+        [ExcludeFromCodeCoverage, DoesNotReturn]
+        string Default()
+        {
+            string exceptionFormat = ExceptionMessages.UnexpectedRuneUtf8SequenceLength;
+            string message = string.Format(CultureInfo.CurrentCulture, exceptionFormat, length);
 #if NET7_0_OR_GREATER
-                throw new UnreachableException(msg);
+            throw new UnreachableException(message);
 #else
-                throw new InvalidOperationException(msg);
+            throw new InvalidOperationException(message);
 #endif
+
+            return default;
         }
     }
 }