diff --git a/src/stdlib/Builtins.fs b/src/stdlib/Builtins.fs
index 7495f92..6dcb665 100644
--- a/src/stdlib/Builtins.fs
+++ b/src/stdlib/Builtins.fs
@@ -200,6 +200,30 @@ type IExports =
     abstract int: obj -> int
     /// Object to float
     abstract float: obj -> float
+
+    /// Return the largest item in an iterable or the largest of two or more arguments.
+    abstract max: 'T * 'T -> 'T
+    /// Return the largest item in an iterable or the largest of two or more arguments.
+    abstract max: 'T * 'T * 'T -> 'T
+    /// Return the largest item in an iterable or the largest of two or more arguments.
+    abstract max: IEnumerable<'T> -> 'T
+
+    /// Return the smallest item in an iterable or the smallest of two or more arguments.
+    abstract min: 'T * 'T -> 'T
+    /// Return the smallest item in an iterable or the smallest of two or more arguments.
+    abstract min: 'T * 'T * 'T -> 'T
+    /// Return the smallest item in an iterable or the smallest of two or more arguments.
+    abstract min: IEnumerable<'T> -> 'T
+
+    /// Return the sum of a 'start' value (default: 0) plus an iterable of numbers.
+    abstract sum: IEnumerable<'T> -> 'T
+
+    /// Return True if bool(x) is True for all values x in the iterable.
+    abstract all: IEnumerable<bool> -> bool
+
+    /// Return True if bool(x) is True for any x in the iterable.
+    abstract any: IEnumerable<bool> -> bool
+
     abstract print: obj: obj -> unit
 
     [<NamedParams(fromIndex = 1)>]
diff --git a/src/stdlib/Os.fs b/src/stdlib/Os.fs
index e482e3e..d366bce 100644
--- a/src/stdlib/Os.fs
+++ b/src/stdlib/Os.fs
@@ -84,6 +84,18 @@ and [<Erase>] PathModule =
     /// Return the base name of pathname path
     /// See https://docs.python.org/3/library/os.path.html#os.path.basename
     abstract basename: path: string -> string
+    /// Return the argument with an initial component of ~ or ~user replaced
+    /// See https://docs.python.org/3/library/os.path.html#os.path.expanduser
+    abstract expanduser: path: string -> string
+    /// Return a normalized absolutized version of the pathname path
+    /// See https://docs.python.org/3/library/os.path.html#os.path.abspath
+    abstract abspath: path: string -> string
+    /// Split the pathname path into a pair (head, tail)
+    /// See https://docs.python.org/3/library/os.path.html#os.path.split
+    abstract split: path: string -> string * string
+    /// Split the pathname path into a pair (root, ext)
+    /// See https://docs.python.org/3/library/os.path.html#os.path.splitext
+    abstract splitext: path: string -> string * string
 
 
 /// Miscellaneous operating system interfaces
diff --git a/test/Fable.Python.Test.fsproj b/test/Fable.Python.Test.fsproj
index fce4bbc..bdd274b 100644
--- a/test/Fable.Python.Test.fsproj
+++ b/test/Fable.Python.Test.fsproj
@@ -16,6 +16,7 @@
     <Compile Include="TestAst.fs" />
     <Compile Include="TestAsyncIO.fs" />
     <Compile Include="TestBuiltins.fs" />
+    <Compile Include="TestOs.fs" />
     <Compile Include="TestJson.fs" />
     <Compile Include="TestString.fs" />
     <Compile Include="Main.fs" />
diff --git a/test/TestBuiltins.fs b/test/TestBuiltins.fs
index 6d6206c..8b489cc 100644
--- a/test/TestBuiltins.fs
+++ b/test/TestBuiltins.fs
@@ -2,6 +2,7 @@ module Fable.Python.Tests.Builtins
 
 open Util.Testing
 open Fable.Python.Builtins
+open Fable.Python.Os
 
 [<Fact>]
 let ``test print works`` () =
@@ -12,5 +13,55 @@ let ``test __name__ works`` () = __name__ |> equal "test_builtins"
 
 [<Fact>]
 let ``test write works`` () =
-    let result = builtins.``open``("test.txt", OpenTextMode.Write)
+    let tempFile = os.path.join (os.path.expanduser "~", ".fable_test_temp.txt")
+    let result = builtins.``open``(tempFile, OpenTextMode.Write)
     result.write "ABC" |> equal 3
+    result.Dispose()
+    os.remove tempFile
+
+[<Fact>]
+let ``test max with two arguments works`` () =
+    builtins.max (3, 5) |> equal 5
+    builtins.max (10, 2) |> equal 10
+
+[<Fact>]
+let ``test max with three arguments works`` () =
+    builtins.max (3, 5, 1) |> equal 5
+    builtins.max (1, 2, 10) |> equal 10
+
+[<Fact>]
+let ``test max with iterable works`` () =
+    builtins.max [1; 2; 3; 4; 5] |> equal 5
+    builtins.max [10; -5; 3] |> equal 10
+
+[<Fact>]
+let ``test min with two arguments works`` () =
+    builtins.min (3, 5) |> equal 3
+    builtins.min (10, 2) |> equal 2
+
+[<Fact>]
+let ``test min with three arguments works`` () =
+    builtins.min (3, 5, 1) |> equal 1
+    builtins.min (1, 2, 10) |> equal 1
+
+[<Fact>]
+let ``test min with iterable works`` () =
+    builtins.min [1; 2; 3; 4; 5] |> equal 1
+    builtins.min [10; -5; 3] |> equal -5
+
+[<Fact>]
+let ``test sum works`` () =
+    builtins.sum [1; 2; 3; 4; 5] |> equal 15
+    builtins.sum [10; -5; 3] |> equal 8
+
+[<Fact>]
+let ``test all works`` () =
+    builtins.all [true; true; true] |> equal true
+    builtins.all [true; false; true] |> equal false
+    builtins.all [] |> equal true
+
+[<Fact>]
+let ``test any works`` () =
+    builtins.any [false; false; true] |> equal true
+    builtins.any [false; false; false] |> equal false
+    builtins.any [] |> equal false
diff --git a/test/TestJson.fs b/test/TestJson.fs
index 76912cc..7e4fb3b 100644
--- a/test/TestJson.fs
+++ b/test/TestJson.fs
@@ -20,3 +20,33 @@ let ``test json loads works`` () =
     let object = {| Foo = 10; Bar = "test" |}
     let result: {| Foo: int; Bar: string |} = unbox (json.loads input)
     result |> equal object
+
+[<Fact>]
+let ``test json.dumps with nativeint works`` () =
+    let value: nativeint = 42n
+    let result = json.dumps value
+    result |> equal "42"
+
+[<Fact>]
+let ``test json.dumps with ResizeArray of nativeint works`` () =
+    let values = ResizeArray([1n; 2n; 3n])
+    let result = json.dumps values
+    result |> equal "[1, 2, 3]"
+
+[<Fact>]
+let ``test json.dumps with nested object works`` () =
+    let obj = {| Name = "test"; Values = ResizeArray([1n; 2n; 3n]) |}
+    let result = dumps obj
+    result |> equal """{"Name": "test", "Values": [1, 2, 3]}"""
+
+[<Fact>]
+let ``test json.loads with array works`` () =
+    let input = "[1, 2, 3]"
+    let result: int array = unbox (json.loads input)
+    result.Length |> equal 3
+
+[<Fact>]
+let ``test json.dumps with indent works`` () =
+    let obj = {| A = 1n |}
+    let result = dumpsIndented obj 2
+    result.Contains("\n") |> equal true
diff --git a/test/TestOs.fs b/test/TestOs.fs
new file mode 100644
index 0000000..8197f6d
--- /dev/null
+++ b/test/TestOs.fs
@@ -0,0 +1,61 @@
+module Fable.Python.Tests.Os
+
+open Util.Testing
+open Fable.Python.Os
+
+[<Fact>]
+let ``test os.path.exists works`` () =
+    os.path.exists "." |> equal true
+    os.path.exists "nonexistent_path_xyz" |> equal false
+
+[<Fact>]
+let ``test os.path.isdir works`` () =
+    os.path.isdir "." |> equal true
+
+[<Fact>]
+let ``test os.path.join works`` () =
+    os.path.join ("a", "b", "c") |> equal "a/b/c"
+
+[<Fact>]
+let ``test os.path.dirname works`` () =
+    os.path.dirname "/foo/bar/baz.txt" |> equal "/foo/bar"
+
+[<Fact>]
+let ``test os.path.basename works`` () =
+    os.path.basename "/foo/bar/baz.txt" |> equal "baz.txt"
+
+[<Fact>]
+let ``test os.path.expanduser works`` () =
+    let expanded = os.path.expanduser "~"
+    // The expanded path should not start with ~ anymore
+    expanded.StartsWith("~") |> equal false
+
+[<Fact>]
+let ``test os.path.abspath works`` () =
+    let absPath = os.path.abspath "."
+    // Absolute path should start with /
+    absPath.StartsWith("/") |> equal true
+
+[<Fact>]
+let ``test os.path.split works`` () =
+    let head, tail = os.path.split "/foo/bar/baz.txt"
+    head |> equal "/foo/bar"
+    tail |> equal "baz.txt"
+
+[<Fact>]
+let ``test os.path.splitext works`` () =
+    let root, ext = os.path.splitext "/foo/bar/baz.txt"
+    root |> equal "/foo/bar/baz"
+    ext |> equal ".txt"
+
+[<Fact>]
+let ``test os.getcwd works`` () =
+    let cwd = os.getcwd ()
+    // Current working directory should be a non-empty string
+    cwd.Length > 0 |> equal true
+
+[<Fact>]
+let ``test os.listdir works`` () =
+    let entries = os.listdir "."
+    // Current directory should have at least some entries
+    entries.Length > 0 |> equal true