diff --git a/pkg/picol/commands.go b/pkg/picol/commands.go
index a1b8d7a..1c21af3 100644
--- a/pkg/picol/commands.go
+++ b/pkg/picol/commands.go
@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
-	"testing"
 )
 
 /*
@@ -18,9 +17,9 @@ func incorrectArgCountError(i *Interpreter, name string, argv []string) error {
 }
 
 /*
- * needleInHaystack returns true if the string is in a slice
+ * NeedleInHaystack returns true if the string is in a slice
  */
-func needleInHaystack(needle string, haystack []string) bool {
+func NeedleInHaystack(needle string, haystack []string) bool {
 	for _, haystackMember := range haystack {
 		if haystackMember == needle {
 			return true
@@ -29,27 +28,6 @@ func needleInHaystack(needle string, haystack []string) bool {
 	return false
 }
 
-/*
- * Test_needleInHaystack tests the return value of needleInHaystack
- */
-func Test_needleInHaystack(t *testing.T) {
-	var haystack = []string{"a", "b", "c"}
-	var needle = "a"
-	if !needleInHaystack(needle, haystack) {
-		t.Errorf("%s not in %s", needle, haystack)
-	}
-
-	needle = "j"
-	if needleInHaystack(needle, haystack) {
-		t.Errorf("%s in %s", needle, haystack)
-	}
-
-	needle = "ab"
-	if needleInHaystack(needle, haystack) {
-		t.Errorf("%s in %s", needle, haystack)
-	}
-}
-
 /*
  * CommandMath is the math command for TCL
  */
@@ -274,7 +252,7 @@ func CommandPuts(i *Interpreter, argv []string, pd interface{}) (string, error)
 /*
  * RegisterCoreCommands is a callable to register TCL commands.
  */
-func (i *Interpreter) RegisterCoreCommands() {
+func (i *Interpreter) RegisterCoreCommands() error {
 	name := [...]string{"+", "-", "*", "/", ">", ">=", "<", "<=", "==", "!="}
 	for _, n := range name {
 		_ = i.RegisterCommand(n, CommandMath, nil)
@@ -289,4 +267,6 @@ func (i *Interpreter) RegisterCoreCommands() {
 	_ = i.RegisterCommand("return", CommandReturn, nil)
 	_ = i.RegisterCommand("error", CommandError, nil)
 	_ = i.RegisterCommand("puts", CommandPuts, nil)
+
+	return nil
 }
diff --git a/pkg/picol/commands_test.go b/pkg/picol/commands_test.go
new file mode 100644
index 0000000..66e8ed8
--- /dev/null
+++ b/pkg/picol/commands_test.go
@@ -0,0 +1,300 @@
+package picol_test
+
+import (
+	"testing"
+
+	"github.com/dragonheim/gagent/pkg/picol"
+)
+
+func Test_NeedleInHaystack(t *testing.T) {
+	var haystack = []string{"a", "b", "c"}
+	var needle = "a"
+	if !picol.NeedleInHaystack(needle, haystack) {
+		t.Errorf("%s not in %s", needle, haystack)
+	}
+
+	needle = "j"
+	if picol.NeedleInHaystack(needle, haystack) {
+		t.Errorf("%s in %s", needle, haystack)
+	}
+
+	needle = "ab"
+	if picol.NeedleInHaystack(needle, haystack) {
+		t.Errorf("%s in %s", needle, haystack)
+	}
+}
+
+func Test_CommandMath(t *testing.T) {
+	// You can add more test cases for various operations and edge cases
+	testCases := []struct {
+		argv   []string
+		result string
+		err    error
+	}{
+		{[]string{"+", "2", "3"}, "5", nil},
+		{[]string{"-", "8", "3"}, "5", nil},
+		{[]string{"*", "2", "3"}, "6", nil},
+		{[]string{"/", "6", "3"}, "2", nil},
+		{[]string{">", "4", "2"}, "1", nil},
+	}
+
+	i := picol.NewInterpreter()
+	for _, tc := range testCases {
+		result, err := picol.CommandMath(i, tc.argv, nil)
+		if result != tc.result || (err != nil && tc.err != nil && err.Error() != tc.err.Error()) {
+			t.Errorf("CommandMath(%v) = (%v, %v); expected (%v, %v)", tc.argv, result, err, tc.result, tc.err)
+		}
+	}
+}
+
+func Test_CommandSet(t *testing.T) {
+	testCases := []struct {
+		argv   []string
+		result string
+		err    error
+	}{
+		{[]string{"set", "x", "42"}, "42", nil},
+		{[]string{"set", "y", "abc"}, "abc", nil},
+	}
+
+	i := picol.NewInterpreter()
+	for _, tc := range testCases {
+		result, err := picol.CommandSet(i, tc.argv, nil)
+		if result != tc.result || (err != nil && tc.err != nil && err.Error() != tc.err.Error()) {
+			t.Errorf("CommandSet(%v) = (%v, %v); expected (%v, %v)", tc.argv, result, err, tc.result, tc.err)
+		}
+	}
+}
+
+func Test_CommandUnset(t *testing.T) {
+	testCases := []struct {
+		argv   []string
+		result string
+		err    error
+	}{
+		{[]string{"unset", "x"}, "", nil},
+		{[]string{"unset", "y"}, "", nil},
+	}
+
+	i := picol.NewInterpreter()
+	i.SetVariable("x", "42")
+	i.SetVariable("y", "abc")
+
+	for _, tc := range testCases {
+		result, err := picol.CommandUnset(i, tc.argv, nil)
+		if result != tc.result || (err != nil && tc.err != nil && err.Error() != tc.err.Error()) {
+			t.Errorf("CommandUnset(%v) = (%v, %v); expected (%v, %v)", tc.argv, result, err, tc.result, tc.err)
+		}
+	}
+}
+
+func Test_CommandIf(t *testing.T) {
+	testCases := []struct {
+		argv   []string
+		result string
+		err    error
+	}{
+		{[]string{"unset", "x"}, "", nil},
+		{[]string{"unset", "y"}, "", nil},
+	}
+
+	i := picol.NewInterpreter()
+	i.SetVariable("x", "42")
+	i.SetVariable("y", "abc")
+
+	for _, tc := range testCases {
+		result, err := picol.CommandUnset(i, tc.argv, nil)
+		if result != tc.result || (err != nil && tc.err != nil && err.Error() != tc.err.Error()) {
+			t.Errorf("CommandUnset(%v) = (%v, %v); expected (%v, %v)", tc.argv, result, err, tc.result, tc.err)
+		}
+	}
+}
+
+func Test_CommandWhile(t *testing.T) {
+	i := picol.NewInterpreter()
+
+	// Test simple while loop
+	err := i.RegisterCoreCommands()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	script := `
+	set i 0
+	set result 0
+	while { < $i 5 } {
+		set result [+ $result $i]
+		set i [+ $i 1]
+	}
+	`
+
+	res, err := i.Eval(script)
+	if err != nil {
+		t.Fatalf("Error during while loop evaluation: %s", err)
+	}
+
+	expectedResult := "10"
+	if res != expectedResult {
+		t.Errorf("Expected %s, got %s", expectedResult, res)
+	}
+
+	// Test nested while loops
+	script = `
+	set i 0
+	set j 0
+	set result 0
+	while { < $i 3 } {
+		set j 0
+		while { < $j 3 } {
+			set result [+ $result $j]
+			set j [+ $j 1]
+		}
+		set i [+ $i 1]
+	}
+	`
+
+	res, err = i.Eval(script)
+	if err != nil {
+		t.Fatalf("Error during nested while loop evaluation: %s", err)
+	}
+
+	expectedResult = "9"
+	if res != expectedResult {
+		t.Errorf("Expected %s, got %s", expectedResult, res)
+	}
+}
+
+// You can also add test functions for other commands like CommandProc, CommandReturn, etc.
+func Test_CommandRetCodes(t *testing.T) {
+	i := picol.NewInterpreter()
+
+	err := i.RegisterCoreCommands()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Test break
+	script := `
+	while { 1 } {
+		break
+	}
+	`
+	_, err = i.Eval(script)
+	if err != nil {
+		t.Fatalf("Error during break evaluation: %s", err)
+	}
+
+	// Test continue
+	script = `
+	set i 0
+	set result 0
+	while { < $i 5 } {
+		if { == $i 2 } {
+			continue
+		}
+		set result [+ $result $i]
+		set i [+ $i 1]
+	}
+	`
+	expectedResult := "7"
+	res, err := i.Eval(script)
+	if err != nil {
+		t.Fatalf("Error during continue evaluation: %s", err)
+	}
+	if res != expectedResult {
+		t.Errorf("Expected %s, got %s", expectedResult, res)
+	}
+}
+
+func Test_CommandProc(t *testing.T) {
+	i := picol.NewInterpreter()
+
+	err := i.RegisterCoreCommands()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	script := `
+	proc sum {a b} {
+		return [+ $a $b]
+	}
+	set res [sum 3 4]
+	`
+	expectedResult := "7"
+	res, err := i.Eval(script)
+	if err != nil {
+		t.Fatalf("Error during proc evaluation: %s", err)
+	}
+	if res != expectedResult {
+		t.Errorf("Expected %s, got %s", expectedResult, res)
+	}
+}
+
+func Test_CommandReturn(t *testing.T) {
+	i := picol.NewInterpreter()
+
+	err := i.RegisterCoreCommands()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	script := `
+	proc testReturn {val} {
+		return $val
+	}
+	set res [testReturn 42]
+	`
+	expectedResult := "42"
+	res, err := i.Eval(script)
+	if err != nil {
+		t.Fatalf("Error during return evaluation: %s", err)
+	}
+	if res != expectedResult {
+		t.Errorf("Expected %s, got %s", expectedResult, res)
+	}
+}
+
+func Test_CommandError(t *testing.T) {
+	i := picol.NewInterpreter()
+
+	err := i.RegisterCoreCommands()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	script := `
+	error "An error occurred"
+	`
+	_, err = i.Eval(script)
+	if err == nil || err.Error() != "An error occurred" {
+		t.Fatalf("Error not raised or incorrect error message: %s", err)
+	}
+}
+
+func Test_CommandPuts(t *testing.T) {
+	i := picol.NewInterpreter()
+
+	err := i.RegisterCoreCommands()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// The following test checks if the "puts" command runs without any error.
+	// However, it doesn't check the printed output since it's not straightforward to capture stdout in tests.
+	script := `
+	puts "Hello, world!"
+	`
+	_, err = i.Eval(script)
+	if err != nil {
+		t.Fatalf("Error during puts evaluation: %s", err)
+	}
+}
+
+func Test_RegisterCoreCommands(t *testing.T) {
+	i := picol.NewInterpreter()
+
+	err := i.RegisterCoreCommands()
+	if err != nil {
+		t.Fatalf("Error during core command registration: %s", err)
+	}
+}
diff --git a/pkg/picol/parser.go b/pkg/picol/parser.go
index e2cbb8b..f2cc441 100644
--- a/pkg/picol/parser.go
+++ b/pkg/picol/parser.go
@@ -7,13 +7,13 @@ import (
 
 // Define parser token types
 const (
-	ptESC = iota
-	ptSTR
-	ptCMD
-	ptVAR
-	ptSEP
-	ptEOL
-	ptEOF
+	ParserTokenESC = iota
+	ParserTokenSTR
+	ParserTokenCMD
+	ParserTokenVAR
+	ParserTokenSEP
+	ParserTokenEOL
+	ParserTokenEOF
 )
 
 // parserStruct represents the parser state
@@ -26,7 +26,7 @@ type parserStruct struct {
 
 // initParser initializes a new parserStruct instance
 func initParser(text string) *parserStruct {
-	return &parserStruct{text: text, ln: len(text), Type: ptEOL}
+	return &parserStruct{text: text, ln: len(text), Type: ParserTokenEOL}
 }
 
 // next advances the parser position by one rune
@@ -57,7 +57,7 @@ func (p *parserStruct) parseSep() string {
 		}
 	}
 	p.end = p.p
-	p.Type = ptSEP
+	p.Type = ParserTokenSEP
 	return p.token()
 }
 
@@ -74,7 +74,7 @@ func (p *parserStruct) parseEol() string {
 	}
 
 	p.end = p.p
-	p.Type = ptEOL
+	p.Type = ParserTokenEOL
 	return p.token()
 }
 
@@ -105,7 +105,7 @@ Loop:
 		p.next()
 	}
 	p.end = p.p
-	p.Type = ptCMD
+	p.Type = ParserTokenCMD
 	if p.p < len(p.text) && p.current() == ']' {
 		p.next()
 	}
@@ -118,7 +118,7 @@ func (p *parserStruct) parseVar() string {
 	p.start = p.p
 
 	if p.current() == '{' {
-		p.Type = ptVAR
+		p.Type = ParserTokenVAR
 		return p.parseBrace()
 	}
 
@@ -134,10 +134,10 @@ func (p *parserStruct) parseVar() string {
 	if p.start == p.p { // It's just a single char string "$"
 		p.start = p.p - 1
 		p.end = p.p
-		p.Type = ptSTR
+		p.Type = ParserTokenSTR
 	} else {
 		p.end = p.p
-		p.Type = ptVAR
+		p.Type = ParserTokenVAR
 	}
 	return p.token()
 }
@@ -173,10 +173,10 @@ Loop:
 
 // parseString parses a string with or without quotes
 func (p *parserStruct) parseString() string {
-	newword := p.Type == ptSEP || p.Type == ptEOL || p.Type == ptSTR
+	newword := p.Type == ParserTokenSEP || p.Type == ParserTokenEOL || p.Type == ParserTokenSTR
 
 	if c := p.current(); newword && c == '{' {
-		p.Type = ptSTR
+		p.Type = ParserTokenSTR
 		return p.parseBrace()
 	} else if newword && c == '"' {
 		p.insidequote = 1
@@ -197,7 +197,7 @@ Loop:
 		case '"':
 			if p.insidequote != 0 {
 				p.end = p.p
-				p.Type = ptESC
+				p.Type = ParserTokenESC
 				p.next()
 				p.insidequote = 0
 				return p.token()
@@ -211,7 +211,7 @@ Loop:
 	}
 
 	p.end = p.p
-	p.Type = ptESC
+	p.Type = ParserTokenESC
 	return p.token()
 }
 
@@ -227,10 +227,10 @@ func (p *parserStruct) parseComment() string {
 func (p *parserStruct) GetToken() string {
 	for {
 		if p.ln == 0 {
-			if p.Type != ptEOL && p.Type != ptEOF {
-				p.Type = ptEOL
+			if p.Type != ParserTokenEOL && p.Type != ParserTokenEOF {
+				p.Type = ParserTokenEOL
 			} else {
-				p.Type = ptEOF
+				p.Type = ParserTokenEOF
 			}
 			return p.token()
 		}
@@ -251,7 +251,7 @@ func (p *parserStruct) GetToken() string {
 		case '$':
 			return p.parseVar()
 		case '#':
-			if p.Type == ptEOL {
+			if p.Type == ParserTokenEOL {
 				p.parseComment()
 				continue
 			}
diff --git a/pkg/picol/parser_test.go b/pkg/picol/parser_test.go
new file mode 100644
index 0000000..a5247f7
--- /dev/null
+++ b/pkg/picol/parser_test.go
@@ -0,0 +1,79 @@
+package picol_test
+
+import (
+	"testing"
+
+	"github.com/dragonheim/gagent/pkg/picol"
+)
+
+func TestParser(t *testing.T) {
+	testCases := []struct {
+		name     string
+		input    string
+		expected []int
+	}{
+		{
+			"Simple test",
+			"set x 10\nincr x",
+			[]int{
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenSTR,
+				picol.ParserTokenEOL,
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenSTR,
+				picol.ParserTokenEOL,
+				picol.ParserTokenEOF,
+			},
+		},
+		{
+			"Variable and command test",
+			"set x $y\nputs [expr $x * 2]",
+			[]int{
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenVAR,
+				picol.ParserTokenEOL,
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenCMD,
+				picol.ParserTokenEOL,
+				picol.ParserTokenEOF,
+			},
+		},
+		{
+			"Braces and quotes test",
+			`set x {"Hello World"}`,
+			[]int{
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenSTR,
+				picol.ParserTokenSEP,
+				picol.ParserTokenSTR,
+				picol.ParserTokenEOL,
+				picol.ParserTokenEOF,
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			parser := picol.InitParser(tc.input)
+
+			for _, expectedType := range tc.expected {
+				token := parser.GetToken()
+				if parser.Type != expectedType {
+					t.Errorf("Expected token type %d, got %d", expectedType, parser.Type)
+				}
+				if parser.Type == picol.ParserTokenEOF {
+					break
+				}
+			}
+		})
+	}
+}
diff --git a/pkg/picol/picol.go b/pkg/picol/picol.go
index 5b53ecb..7390d5f 100644
--- a/pkg/picol/picol.go
+++ b/pkg/picol/picol.go
@@ -125,33 +125,33 @@ func (interp *Interpreter) Eval(script string) (string, error) {
 	for {
 		prevType := parser.Type
 		token := parser.GetToken()
-		if parser.Type == ptEOF {
+		if parser.Type == ParserTokenEOF {
 			break
 		}
 
 		switch parser.Type {
-		case ptVAR:
+		case ParserTokenVAR:
 			v, ok := interp.Variable(token)
 			if !ok {
 				return "", fmt.Errorf("no such variable '%s'", token)
 			}
 			token = string(v)
-		case ptCMD:
+		case ParserTokenCMD:
 			result, err = interp.Eval(token)
 			if err != nil {
 				return result, err
 			}
 			token = result
-		case ptESC:
+		case ParserTokenESC:
 			/*
 			 * TODO: escape handling missing!
 			 */
-		case ptSEP:
+		case ParserTokenSEP:
 			// prevType = parser.Type
 			continue
 		}
 
-		if parser.Type == ptEOL {
+		if parser.Type == ParserTokenEOL {
 			// prevType = parser.Type
 			if len(argv) != 0 {
 				cmd := interp.Command(argv[0])
@@ -173,7 +173,7 @@ func (interp *Interpreter) Eval(script string) (string, error) {
 		/*
 		 * We have a new token, append to the previous or as new arg?
 		 */
-		if prevType == ptSEP || prevType == ptEOL {
+		if prevType == ParserTokenSEP || prevType == ParserTokenEOL {
 			argv = append(argv, token)
 		} else { // Interpolation
 			argv[len(argv)-1] = strings.Join([]string{argv[len(argv)-1], token}, "")
diff --git a/pkg/picol/picol_test.go b/pkg/picol/picol_test.go
new file mode 100644
index 0000000..3137dcc
--- /dev/null
+++ b/pkg/picol/picol_test.go
@@ -0,0 +1,56 @@
+package picol_test
+
+import (
+	"testing"
+
+	"github.com/dragonheim/gagent/pkg/picol"
+)
+
+func TestInterpreter(t *testing.T) {
+	interp := picol.NewInterpreter()
+
+	// Register a command
+	err := interp.RegisterCommand("test", testCommand, nil)
+	if err != nil {
+		t.Fatalf("Error registering test command: %v", err)
+	}
+
+	// Test command execution
+	script := "test hello world"
+	result, err := interp.Eval(script)
+	if err != nil {
+		t.Fatalf("Error executing script: %v", err)
+	}
+	expected := "hello world"
+	if result != expected {
+		t.Errorf("Expected result '%s', got '%s'", expected, result)
+	}
+
+	// Test variable setting
+	interp.SetVariable("x", "42")
+
+	// Test variable retrieval
+	val, ok := interp.Variable("x")
+	if !ok {
+		t.Fatalf("Variable 'x' not found")
+	}
+	expectedVar := "42"
+	if val != picol.Variable(expectedVar) {
+		t.Errorf("Expected variable value '%s', got '%s'", expectedVar, val)
+	}
+
+	// Test variable unsetting
+	interp.UnsetVariable("x")
+	_, ok = interp.Variable("x")
+	if ok {
+		t.Fatalf("Variable 'x' should have been unset")
+	}
+}
+
+// testCommand is a simple custom command for testing
+func testCommand(interp *picol.Interpreter, argv []string, privdata interface{}) (string, error) {
+	if len(argv) != 3 {
+		return "", nil
+	}
+	return argv[1] + " " + argv[2], nil
+}
diff --git a/pkg/picol/picol_unused/main.go_unused b/pkg/picol/picol_unused/main.go_unused
index c1fb8fa..4db8dd1 100644
--- a/pkg/picol/picol_unused/main.go_unused
+++ b/pkg/picol/picol_unused/main.go_unused
@@ -12,16 +12,15 @@ import (
 
 var fname = flag.String("f", "", "file name")
 
-func main() {
-	flag.Parse()
+func RunPicol(fname string) error {
 	interp := picol.NewInterpreter()
 	interp.RegisterCoreCommands()
 
-	buf, err := ioutil.ReadFile(*fname)
+	buf, err := ioutil.ReadFile(fname)
 	if err == nil {
 		result, err := interp.Eval(string(buf))
 		if err != nil {
-			fmt.Println("ERRROR", result, err)
+			return fmt.Errorf("Error: %s, Result: %s", err, result)
 		}
 	} else {
 		for {
@@ -30,8 +29,17 @@ func main() {
 			clibuf, _ := scanner.ReadString('\n')
 			result, err := interp.Eval(clibuf[:len(clibuf)-1])
 			if len(result) != 0 {
-				fmt.Println("ERRROR", result, err)
+				return fmt.Errorf("Error: %s, Result: %s", err, result)
 			}
 		}
 	}
+	return nil
+}
+
+func main() {
+	flag.Parse()
+	err := RunPicol(*fname)
+	if err != nil {
+		fmt.Println(err)
+	}
 }
diff --git a/pkg/picol/picol_unused/main_test.go_unused b/pkg/picol/picol_unused/main_test.go_unused
new file mode 100644
index 0000000..896671d
--- /dev/null
+++ b/pkg/picol/picol_unused/main_test.go_unused
@@ -0,0 +1,31 @@
+package main_test
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	picol "github.com/dragonheim/gagent/pkg/picol/picol_unused"
+)
+
+func Test_RunPicol(t *testing.T) {
+	// Create a temporary test file
+	content := []byte("set a 5\nset b 7\n+ $a $b\n")
+	tmpfile, err := ioutil.TempFile("", "picol_test")
+	if err != nil {
+		t.Fatalf("Error creating temporary test file: %v", err)
+	}
+	defer os.Remove(tmpfile.Name()) // clean up
+
+	if _, err := tmpfile.Write(content); err != nil {
+		t.Fatalf("Error writing content to temporary test file: %v", err)
+	}
+	if err := tmpfile.Close(); err != nil {
+		t.Fatalf("Error closing temporary test file: %v", err)
+	}
+
+	err = picol.RunPicol(tmpfile.Name())
+	if err != nil {
+		t.Errorf("Error during RunPicol: %v", err)
+	}
+}