diff --git a/tests/FSharp.Data.Core.Tests/FSharp.Data.Core.Tests.fsproj b/tests/FSharp.Data.Core.Tests/FSharp.Data.Core.Tests.fsproj
index f583f64ed..f156734b1 100644
--- a/tests/FSharp.Data.Core.Tests/FSharp.Data.Core.Tests.fsproj
+++ b/tests/FSharp.Data.Core.Tests/FSharp.Data.Core.Tests.fsproj
@@ -21,6 +21,7 @@
     <Compile Include="Http.fs" />
     <Compile Include="HttpRequestHeaders.fs" />
     <Compile Include="NameUtils.fs" />
+    <Compile Include="Pluralizer.fs" />
     <Compile Include="IOTests.fs" />
     <Compile Include="TextConversions.fs" />
     <Compile Include="Caching.fs" />
diff --git a/tests/FSharp.Data.Core.Tests/Pluralizer.fs b/tests/FSharp.Data.Core.Tests/Pluralizer.fs
new file mode 100644
index 000000000..cbe07d2d2
--- /dev/null
+++ b/tests/FSharp.Data.Core.Tests/Pluralizer.fs
@@ -0,0 +1,223 @@
+// --------------------------------------------------------------------------------------
+// Tests for the Pluralizer module that handles English noun pluralization
+// --------------------------------------------------------------------------------------
+
+module FSharp.Data.Tests.Pluralizer
+
+open FsUnit
+open NUnit.Framework
+open FSharp.Data.Runtime.Pluralizer
+
+[<Test>]
+let ``toPlural handles null and empty strings`` () = 
+    toPlural null |> should equal null
+    toPlural "" |> should equal ""
+    toPlural "   " |> should not' (equal "   ")  // Should trim and process
+
+[<Test>]
+let ``toSingular handles null and empty strings`` () = 
+    toSingular null |> should equal null
+    toSingular "" |> should equal ""
+    toSingular "   " |> should equal "   "  // Whitespace is preserved
+
+[<Test>]
+let ``Basic suffix rules work correctly`` () =
+    // Test common suffix rules
+    toPlural "church" |> should equal "churches"
+    toPlural "flash" |> should equal "flashes"
+    toPlural "class" |> should equal "classes"
+    
+    toPlural "boy" |> should equal "boys"
+    toPlural "key" |> should equal "keys"
+    toPlural "city" |> should equal "cities"  // y -> ies rule
+    
+    toPlural "hero" |> should equal "heroes"
+    toPlural "photo" |> should equal "photos"  // Should use special word rule
+    
+    toPlural "house" |> should equal "houses"  // Special case
+    toPlural "course" |> should equal "courses"  // Special case
+
+[<Test>]
+let ``Complex suffix rules work correctly`` () =
+    toPlural "crisis" |> should equal "crises"
+    toPlural "campus" |> should equal "campuses"
+    toPlural "basis" |> should equal "bases"
+    toPlural "axis" |> should equal "axes"
+    
+    toPlural "louse" |> should equal "lice"
+    toPlural "mouse" |> should equal "mice"
+    
+    toPlural "zoon" |> should equal "zoa"
+    toPlural "man" |> should equal "men"
+
+[<Test>]
+let ``Words ending with f/fe become ves`` () =
+    toPlural "half" |> should equal "halves"
+    toPlural "elf" |> should equal "elves"
+    toPlural "wolf" |> should equal "wolves"
+    toPlural "scarf" |> should equal "scarves"
+    
+    toPlural "knife" |> should equal "knives"
+    toPlural "life" |> should equal "lives" 
+    toPlural "wife" |> should equal "wives"
+
+[<Test>]
+let ``Irregular plurals from special words list`` () =
+    toPlural "child" |> should equal "children"
+    toPlural "foot" |> should equal "feet"
+    toPlural "tooth" |> should equal "teeth"
+    toPlural "goose" |> should equal "geese"
+    
+    toPlural "deer" |> should equal "deer"  // Unchanged
+    toPlural "sheep" |> should equal "sheep"  // Unchanged
+    toPlural "fish" |> should equal "fishes"  // Can be "fish" or "fishes", this uses suffix rule
+
+[<Test>]
+let ``Scientific and foreign words`` () =
+    toPlural "bacterium" |> should equal "bacteria"
+    toPlural "datum" |> should equal "data"
+    toPlural "alumnus" |> should equal "alumni"
+    toPlural "alumna" |> should equal "alumnae"
+    toPlural "apex" |> should equal "apices"
+    toPlural "vertex" |> should equal "vertices"
+    toPlural "index" |> should equal "indices"
+
+[<Test>]
+let ``Words that don't change in plural`` () =
+    toPlural "aircraft" |> should equal "aircraft"
+    toPlural "chassis" |> should equal "chassis"  
+    toPlural "debris" |> should equal "debris"
+    toPlural "headquarters" |> should equal "headquarters"
+    toPlural "news" |> should equal "news"
+    toPlural "series" |> should equal "series"
+
+[<Test>]
+let ``Case sensitivity is preserved`` () =
+    toPlural "HOUSE" |> should equal "HOUSES"
+    toPlural "House" |> should equal "Houses"
+    toPlural "house" |> should equal "houses"
+    toPlural "HoUsE" |> should equal "Houses"  // Case adjustment follows template
+
+[<Test>]
+let ``Basic singularization works`` () =
+    toSingular "churches" |> should equal "church"
+    toSingular "flashes" |> should equal "flash"
+    toSingular "classes" |> should equal "class"
+    
+    toSingular "cities" |> should equal "city"
+    toSingular "boys" |> should equal "boy"
+    toSingular "keys" |> should equal "key"
+    
+    toSingular "heroes" |> should equal "hero"
+    toSingular "houses" |> should equal "house"
+
+[<Test>]
+let ``Complex singularization works`` () =
+    toSingular "children" |> should equal "child"
+    toSingular "feet" |> should equal "foot"
+    toSingular "teeth" |> should equal "tooth"
+    toSingular "geese" |> should equal "goose"
+    toSingular "mice" |> should equal "mouse"
+    
+    toSingular "bacteria" |> should equal "bacterium"
+    toSingular "data" |> should equal "datum"
+    toSingular "alumni" |> should equal "alumnus"
+
+[<Test>]
+let ``Singularization preserves case`` () =
+    toSingular "HOUSES" |> should equal "HOUSE"
+    toSingular "Houses" |> should equal "House"  
+    toSingular "houses" |> should equal "house"
+    toSingular "HoUsEs" |> should equal "House"  // Case adjustment follows template
+
+[<Test>]
+let ``Words already plural remain plural`` () =
+    toPlural "houses" |> should equal "houses"  // Already plural
+    toPlural "mice" |> should equal "mices"     // Pluralizer doesn't detect this as already plural
+    toPlural "children" |> should equal "childrens"  // Pluralizer doesn't recognize this as already plural
+
+[<Test>]
+let ``Words already singular remain singular`` () =
+    toSingular "house" |> should equal "house"  // Already singular
+    toSingular "mouse" |> should equal "mouse"  // Already singular irregular
+    toSingular "child" |> should equal "child"  // Already singular
+
+[<Test>]
+let ``Default rules for unknown words`` () =
+    // Unknown words should get 's' added
+    toPlural "unknownword" |> should equal "unknownwords"
+    toPlural "newterm" |> should equal "newterms"
+    
+    // Unknown plurals ending in 's' should get 's' removed (if not ending in "us")
+    toSingular "unknownwords" |> should equal "unknownword"
+    toSingular "newterms" |> should equal "newterm"
+    
+    // But "us" endings should remain unchanged
+    toSingular "campus" |> should equal "campus"  // Should not become "campu"
+
+[<Test>]
+let ``Mixed case and edge case handling`` () =
+    // Single letter words
+    toPlural "a" |> should equal "as"
+    toSingular "as" |> should equal "a"
+    
+    // Numbers (should remain unchanged or follow basic rules)
+    toPlural "1" |> should equal "1s"
+    
+    // Words with numbers
+    toPlural "mp3" |> should equal "mp3s"
+    toSingular "mp3s" |> should equal "mp3"
+
+[<Test>]
+let ``Special edge cases from word list`` () =
+    // Test some edge cases from the special words list
+    toPlural "octopus" |> should equal "octopuses"  // First plural form
+    toSingular "octopuses" |> should equal "octopus"
+    toSingular "octopodes" |> should equal "octopus"  // Alternative plural
+    
+    toPlural "focus" |> should equal "focuses"  // First plural form
+    toSingular "focuses" |> should equal "focus"
+    toSingular "foci" |> should equal "focus"  // Alternative plural
+    
+    // Test words with multiple plural forms
+    toPlural "fungus" |> should equal "fungi"  // First plural form in list
+    toSingular "fungi" |> should equal "fungus"
+    toSingular "funguses" |> should equal "fungus"  // Alternative plural
+
+[<Test>]
+let ``Roundtrip consistency for common words`` () =
+    let testWords = [
+        "book"; "house"; "child"; "mouse"; "man"; "woman"
+        "city"; "country"; "company"; "person"; "foot"; "tooth"
+        "deer"; "sheep"; "fish"; "aircraft"; "series"
+    ]
+    
+    for word in testWords do
+        let plural = toPlural word
+        let backToSingular = toSingular plural
+        
+        // For most words, singularizing the plural should get back the original
+        // (This may not be true for all words due to multiple plural forms)
+        if word <> "deer" && word <> "sheep" && word <> "fish" && 
+           word <> "aircraft" && word <> "series" then
+            backToSingular |> should equal word
+
+[<Test>]
+let ``Performance with repeated calls`` () =
+    // Test that repeated calls with same input work correctly (testing lazy initialization)
+    let word = "house"
+    let firstResult = toPlural word
+    let secondResult = toPlural word
+    let thirdResult = toPlural word
+    
+    firstResult |> should equal "houses"
+    secondResult |> should equal firstResult
+    thirdResult |> should equal firstResult
+    
+    // Same for singularization
+    let pluralWord = "houses"
+    let firstSingular = toSingular pluralWord  
+    let secondSingular = toSingular pluralWord
+    
+    firstSingular |> should equal "house"
+    secondSingular |> should equal firstSingular
\ No newline at end of file