Add a simple test case for tokenizer.

internal/tokenizer/tokenize_test.go

@@ -0,0 +1,14 @@
+package tokenizer_test
+
+import (
+	"testing"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/gslin/go-ir-playground/internal/tokenizer"
+)
+
+func testTokenize(t *testing.T) {
+	a := tokenizer.Tokenize("test")
+	assert.Equal(t, len(a), 1)
+	assert.Equal(t, a[0], "test")
+}