Fix TitleCase not capitalizing the first word when it is an article, conjunction, or preposition (#1658)

src/Humanizer.Tests/TransformersTests.cs

@@ -34,4 +34,12 @@ public void TransformToSentenceCase(string input, string expectedOutput) =>
     [InlineData("Title Case", "TITLE CASE")]
     public void TransformToUpperCase(string input, string expectedOutput) =>
         Assert.Equal(expectedOutput, input.Transform(To.UpperCase));
+
+    [Theory]
+    [InlineData("a great article", "A Great Article")]
+    [InlineData("yet another conjunction", "Yet Another Conjunction")]
+    [InlineData("by this preposition", "By This Preposition")]
+    [InlineData("NASA and the future", "NASA and the Future")]
+    public void TransformToTitleCase_FirstWordExceptions(string input, string expectedOutput) =>
+        Assert.Equal(expectedOutput, input.Transform(To.TitleCase));
 }

src/Humanizer/Transformer/ToTitleCase.cs

@@ -10,7 +10,7 @@ public string Transform(string input) =>
 #if NET7_0_OR_GREATER
     [GeneratedRegex(WordPattern)]
     private static partial Regex WordRegexGenerated();
-    
+
     private static Regex WordRegex() => WordRegexGenerated();
 #else
     private static readonly Regex WordRegexDefinition = new(WordPattern, RegexOptions.Compiled);
@@ -23,10 +23,19 @@ public string Transform(string input, CultureInfo culture)
         var matches = WordRegex().Matches(input);
         var builder = new StringBuilder(input);
         var textInfo = culture.TextInfo;
+        var isFirstWord = true;
+
         foreach (Match word in matches)
         {
             var value = word.Value;
-            if (AllCapitals(value) || IsArticleOrConjunctionOrPreposition(value))
+            var currentIsFirst = isFirstWord;
+            isFirstWord = false;
+
+            if (AllCapitals(value))
+            {
+                continue;
+            }
+            if (!currentIsFirst && IsArticleOrConjunctionOrPreposition(value))
             {
                 continue;
             }