diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index fa46f09..61454c6 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -9,7 +9,7 @@ on:
 jobs:
 
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     env:
       VARNAM_UPSTREAM: https://varnam.subinsb.com
 
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 1fa39b7..299cd4b 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         include:
-          - os: ubuntu-18.04
+          - os: ubuntu-20.04
             file: "*.zip"
 
     steps:
diff --git a/govarnam/vst_maker_test.go b/govarnam/vst_maker_test.go
index 7eb6620..3ea926c 100644
--- a/govarnam/vst_maker_test.go
+++ b/govarnam/vst_maker_test.go
@@ -1,8 +1,234 @@
 package govarnam
 
-import "testing"
+import (
+	"context"
+	"path"
+	"strings"
+	"testing"
+)
 
-func TestVM(t *testing.T) {
-	// TODO
-	// varnam := getVarnamInstance("ml")
+// initialize VST Maker for tests
+func initTestVM() (*Varnam, error) {
+	return VMInit(path.Join(testTempDir, "test.vst"))
+}
+
+func TestCreatTokenWithoutBuffering(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	err = varnam.VMCreateToken("pattern", "value1", "value2", "value3", "tag", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+
+	search := NewSearchSymbol()
+	search.Pattern = "pattern"
+	symbols, err := varnam.SearchSymbolTable(context.Background(), search)
+	checkError(err)
+	assertEqual(t, len(symbols) == 1, true)
+}
+
+func TestCreatTokenWithBuffering(t *testing.T) {
+	varnam, err := initTestVM()
+
+	checkError(err)
+	err = varnam.VMCreateToken("pattern1", "value1", "value2", "", "value3", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, true)
+	checkError(err)
+
+	search := NewSearchSymbol()
+	search.Pattern = "pattern1"
+	symbols, err := varnam.SearchSymbolTable(context.Background(), search)
+	checkError(err)
+	assertEqual(t, len(symbols) == 1, true)
+
+	err = varnam.VMFlushBuffer()
+	checkError(err)
+}
+
+func TestDeleteToken(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	search := NewSearchSymbol()
+	search.Pattern = "pattern"
+	err = varnam.VMDeleteToken(search)
+	checkError(err)
+
+	symbols, err := varnam.SearchSymbolTable(context.Background(), search)
+	checkError(err)
+	assertEqual(t, len(symbols) == 0, true)
+
+	search.Pattern = "pattern1"
+	err = varnam.VMDeleteToken(search)
+	checkError(err)
+
+	symbols, err = varnam.SearchSymbolTable(context.Background(), search)
+	checkError(err)
+	assertEqual(t, len(symbols) == 0, true)
+}
+
+func TestGetAllTokens(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	err = varnam.VMCreateToken("pattern", "value1", "value2", "", "", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+
+	err = varnam.VMCreateToken("pattern1", "value11", "value21", "", "", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+
+	err = varnam.VMCreateToken("pattern2", "value12", "value22", "", "", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+
+	varnam.VSTMakerConfig.UseDeadConsonants = false
+
+	err = varnam.VMCreateToken("r", "v", "v", "", "", VARNAM_SYMBOL_CONSONANT, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+
+	err = varnam.VMCreateToken("r", "v12", "v", "", "", VARNAM_SYMBOL_CONSONANT, VARNAM_MATCH_POSSIBILITY, 0, 0, false)
+	checkError(err)
+
+	search := NewSearchSymbol()
+	search.Type = VARNAM_SYMBOL_VOWEL
+
+	symbols, err := varnam.SearchSymbolTable(context.Background(), search)
+	checkError(err)
+	assertEqual(t, len(symbols) == 3, true)
+
+	search.Type = VARNAM_SYMBOL_CONSONANT
+	symbols, err = varnam.SearchSymbolTable(context.Background(), search)
+	checkError(err)
+	assertEqual(t, len(symbols) == 2, true)
+}
+
+func TestSetSchemeDetails(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+	sd := SchemeDetails{
+		LangCode:    "tl",
+		DisplayName: "Test",
+		Author:      "Anon",
+	}
+	err = varnam.VMSetSchemeDetails(sd)
+	checkError(err)
+}
+
+func TestIgnoreDuplicates(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	varnam.VSTMakerConfig.IgnoreDuplicateTokens = false
+
+	// should succeed
+	err = varnam.VMCreateToken("pattern21", "value1", "value2", "value3", "tag", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+
+	// should return error
+	err = varnam.VMCreateToken("pattern21", "value1", "value2", "value3", "tag", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	assertEqual(t, err != nil, true)
+
+	// Ignore Duplicate Tokens
+	varnam.VSTMakerConfig.IgnoreDuplicateTokens = true
+
+	err = varnam.VMCreateToken("pattern21", "value1", "value2", "value3", "tag", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+}
+
+func TestCreateDeadConsonants(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	// Use dead consonants
+	varnam.VSTMakerConfig.UseDeadConsonants = true
+
+	err = varnam.VMCreateToken("~", "്", "", "tag", "", VARNAM_SYMBOL_VIRAMA, VARNAM_MATCH_EXACT, 1, 0, false)
+	checkError(err)
+
+	err = varnam.VMCreateToken("ka", "ക", "", "tag", "", VARNAM_SYMBOL_CONSONANT, VARNAM_MATCH_EXACT, 1, 0, false)
+	checkError(err)
+
+	err = varnam.VMCreateToken("p", "പ്", "", "tag", "value3", VARNAM_SYMBOL_CONSONANT, VARNAM_MATCH_EXACT, 1, 0, false)
+	checkError(err)
+
+	varnam.VMFlushBuffer()
+
+	search := NewSearchSymbol()
+	search.Type = VARNAM_SYMBOL_DEAD_CONSONANT
+
+	symbols, err := varnam.SearchSymbolTable(context.Background(), search)
+	checkError(err)
+
+	deadConsonantFound := false
+	for _, sym := range symbols {
+		if sym.Pattern == "k" {
+			deadConsonantFound = true
+		}
+	}
+	assertEqual(t, deadConsonantFound, true)
+}
+
+func TestCreateExactMatchDuplicates(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	// should be success
+	err = varnam.VMCreateToken("patterna", "value1", "value2", "value3", "tag", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	checkError(err)
+
+	// disable IgnoreDuplicateTokens flag
+	varnam.VSTMakerConfig.IgnoreDuplicateTokens = false
+
+	// should return error
+	err = varnam.VMCreateToken("patterna", "value1", "value2", "value3", "tag", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	assertEqual(t, err != nil, true)
+}
+
+func TestCreatePossibilityMatchDuplicates(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	// disable IgnoreDuplicateTokens flag
+	varnam.VSTMakerConfig.IgnoreDuplicateTokens = false
+
+	err = varnam.VMCreateToken("pattern3", "value1", "value2", "", "value3", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_POSSIBILITY, 0, 0, false)
+	checkError(err)
+
+	// should be allowed since it has different values
+	err = varnam.VMCreateToken("pattern3", "value11", "value22", "", "value3", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_POSSIBILITY, 0, 0, false)
+	checkError(err)
+
+	// should return error
+	err = varnam.VMCreateToken("pattern3", "value1", "value2", "", "value3", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_POSSIBILITY, 0, 0, false)
+	assertEqual(t, err != nil, true)
+}
+
+func TestRestrictInvalidMatchTypes(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	// should return error
+	err = varnam.VMCreateToken("pattern0", "value1", "value2", "", "value3", VARNAM_SYMBOL_VOWEL, 11, 0, 0, false)
+	assertEqual(t, err != nil, true)
+}
+
+func TestMaxLengthCheck(t *testing.T) {
+	varnam, err := initTestVM()
+	checkError(err)
+
+	pattern := strings.Builder{}
+	pattern.Grow(VARNAM_SYMBOL_MAX + 2)
+
+	value1 := strings.Builder{}
+	value1.Grow(VARNAM_SYMBOL_MAX + 2)
+
+	value2 := strings.Builder{}
+	value2.Grow(VARNAM_SYMBOL_MAX + 2)
+
+	// should return error
+	err = varnam.VMCreateToken(pattern.String(), value1.String(), value2.String(), "", "value3", VARNAM_SYMBOL_VOWEL, VARNAM_MATCH_EXACT, 0, 0, false)
+	assertEqual(t, err != nil, true)
+}
+
+// TODO: incomplete API
+func TestPrefixTree(t *testing.T) {
+	// varnam, err := initTestVM()
+	// checkError(err)
 }