diff --git a/src/StringExtensions.cs b/src/StringExtensions.cs
index b4d5665..861e49a 100644
--- a/src/StringExtensions.cs
+++ b/src/StringExtensions.cs
@@ -11,6 +11,12 @@ namespace StringResourceVisualizer
 {
     public static class StringExtensions
     {
+        /// <summary>
+        /// Finds where the first of the values occurs in a text.
+        /// </summary>
+        /// <param name="source">The text to search.</param>
+        /// <param name="values">The values to look for. A value can be in the array more than once.</param>
+        /// <returns>The index of the earliest occurrence of any of the values, or -1 if none of them occurs.</returns>
         public static async Task<int> IndexOfAnyAsync(this string source, params string[] values)
         {
             try
@@ -25,7 +31,9 @@ public static async Task<int> IndexOfAnyAsync(this string source, params string[
 
                 if (valuePositions.Any(v => v.Value > -1))
                 {
-                    var result = valuePositions.Where(v => v.Value > -1).OrderByDescending(v => v.Key.Length).FirstOrDefault().Value;
+                    // The earliest occurrence counts, whatever the length of the value.
+                    // Using the longest value that occurs anywhere in the text would skip a shorter one that comes before it.
+                    var result = valuePositions.Where(v => v.Value > -1).Min(v => v.Value);
 
                     return result;
                 }
@@ -43,6 +51,12 @@ public static async Task<int> IndexOfAnyAsync(this string source, params string[
             return -1;
         }
 
+        /// <summary>
+        /// Finds where each of the values occurs in a text.
+        /// </summary>
+        /// <param name="source">The text to search.</param>
+        /// <param name="values">The values to look for.</param>
+        /// <returns>The index of every occurrence of any of the values, from left to right.</returns>
         public static async Task<List<int>> GetAllIndexesAsync(this string source, params string[] values)
         {
             var result = new List<int>();
diff --git a/src/StringResourceVisualizer.Tests/StringExtensionTests.cs b/src/StringResourceVisualizer.Tests/StringExtensionTests.cs
new file mode 100644
index 0000000..9b87e32
--- /dev/null
+++ b/src/StringResourceVisualizer.Tests/StringExtensionTests.cs
@@ -0,0 +1,133 @@
+// <copyright file="StringExtensionTests.cs" company="Matt Lacey">
+// Copyright (c) Matt Lacey. All rights reserved.
+// </copyright>
+
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace StringResourceVisualizer.Tests
+{
+    [TestClass]
+    public class StringExtensionTests
+    {
+        [TestMethod]
+        public async Task IndexOfAny_NoValues_FindsNothing()
+        {
+            var actual = await "Resources.Greeting".IndexOfAnyAsync();
+
+            Assert.AreEqual(-1, actual);
+        }
+
+        [TestMethod]
+        public async Task IndexOfAny_ValueThatIsNotThere_FindsNothing()
+        {
+            var actual = await "var x = 1;".IndexOfAnyAsync("Resources.");
+
+            Assert.AreEqual(-1, actual);
+        }
+
+        [TestMethod]
+        public async Task IndexOfAny_SearchIsCaseSensitive()
+        {
+            var actual = await "var x = resources.Greeting;".IndexOfAnyAsync("Resources.");
+
+            Assert.AreEqual(-1, actual);
+        }
+
+        [TestMethod]
+        public async Task IndexOfAny_SingleValue_FindsItsFirstOccurrence()
+        {
+            var actual = await "var x = Resources.A + Resources.B;".IndexOfAnyAsync("Resources.");
+
+            Assert.AreEqual(8, actual);
+        }
+
+        [TestMethod]
+        public async Task IndexOfAny_SeveralValues_FindsTheEarliestOne()
+        {
+            var actual = await "Strings.A + Resources.B".IndexOfAnyAsync("Resources.", "Strings.");
+
+            Assert.AreEqual(0, actual);
+        }
+
+        [TestMethod]
+        public async Task IndexOfAny_SeveralValues_FindsTheEarliestOneWhateverTheOrderOfTheValues()
+        {
+            var actual = await "Strings.A + Resources.B".IndexOfAnyAsync("Strings.", "Resources.");
+
+            Assert.AreEqual(0, actual);
+        }
+
+        [TestMethod]
+        public async Task IndexOfAny_SeveralValues_SkipsTheOnesThatAreNotThere()
+        {
+            var actual = await "x = Strings.A".IndexOfAnyAsync("Resources.", "Strings.");
+
+            Assert.AreEqual(4, actual);
+        }
+
+        [TestMethod]
+        public async Task IndexOfAny_DuplicateValues_DoNotMatter()
+        {
+            var actual = await "x = Resources.A".IndexOfAnyAsync("Resources.", "Resources.");
+
+            Assert.AreEqual(4, actual);
+        }
+
+        [TestMethod]
+        public async Task GetAllIndexes_NameBeforeALongerName_IsFound()
+        {
+            var actual = await "Strings.A + Resources.B".GetAllIndexesAsync("Strings.", "Resources.");
+
+            CollectionAssert.AreEqual(new[] { 0, 12 }, actual);
+        }
+
+        [TestMethod]
+        public async Task GetAllIndexes_NameAfterALongerName_IsFound()
+        {
+            var actual = await "Resources.A + Strings.B".GetAllIndexesAsync("Strings.", "Resources.");
+
+            CollectionAssert.AreEqual(new[] { 0, 14 }, actual);
+        }
+
+        [TestMethod]
+        public async Task GetAllIndexes_NamesOfDifferentLengthsInAnyOrder_AreAllFoundFromLeftToRight()
+        {
+            var actual = await "Strings.A, Resources.B, Strings.C".GetAllIndexesAsync("Strings.", "Resources.");
+
+            CollectionAssert.AreEqual(new[] { 0, 11, 24 }, actual);
+        }
+
+        [TestMethod]
+        public async Task GetAllIndexes_EveryUseOfTheSameName_IsFound()
+        {
+            var actual = await "Resources.A + Resources.B".GetAllIndexesAsync("Resources.");
+
+            CollectionAssert.AreEqual(new[] { 0, 14 }, actual);
+        }
+
+        [TestMethod]
+        public async Task GetAllIndexes_NameThatEndsWithAnotherName_FindsBoth()
+        {
+            var actual = await "MyResources.A".GetAllIndexesAsync("Resources.", "MyResources.");
+
+            CollectionAssert.AreEqual(new[] { 0, 2 }, actual);
+        }
+
+        [TestMethod]
+        public async Task GetAllIndexes_NothingFound_IsEmpty()
+        {
+            var actual = await "var x = 1;".GetAllIndexesAsync("Resources.");
+
+            Assert.AreEqual(0, actual.Count);
+        }
+
+        [TestMethod]
+        public async Task GetAllIndexes_NoValues_IsEmpty()
+        {
+            var actual = await "Resources.A".GetAllIndexesAsync();
+
+            Assert.AreEqual(0, actual.Count);
+        }
+    }
+}
diff --git a/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj b/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj
index 82e550c..e47a819 100644
--- a/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj
+++ b/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj
@@ -44,6 +44,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ResourceAdornmentManagerTests.cs" />
+    <Compile Include="StringExtensionTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
   <ItemGroup>