diff --git a/typecheck/builtin/float64_test.go b/typecheck/builtin/float64_test.go
new file mode 100644
index 0000000..f1c10fc
--- /dev/null
+++ b/typecheck/builtin/float64_test.go
@@ -0,0 +1,127 @@
+package builtin_test
+
+import (
+	"fmt"
+	"math"
+	"testing"
+
+	"git.xdrm.io/go/aicra/typecheck/builtin"
+)
+
+func TestFloat64_New(t *testing.T) {
+	t.Parallel()
+
+	inst := interface{}(builtin.NewFloat64())
+
+	switch cast := inst.(type) {
+	case *builtin.Float64:
+		return
+	default:
+		t.Errorf("expect %T ; got %T", &builtin.Float64{}, cast)
+	}
+}
+
+func TestFloat64_AvailableTypes(t *testing.T) {
+	t.Parallel()
+
+	inst := builtin.NewFloat64()
+
+	tests := []struct {
+		Type    string
+		Handled bool
+	}{
+		{"float", true},
+		{"float64", true},
+		{"Float", false},
+		{"Float64", false},
+		{"FLOAT", false},
+		{"FLOAT64", false},
+		{" float", false},
+		{"float ", false},
+		{" float ", false},
+		{" float64", false},
+		{"float64 ", false},
+		{" float64 ", false},
+	}
+
+	for _, test := range tests {
+		t.Run(test.Type, func(t *testing.T) {
+			checker := inst.Checker(test.Type)
+			if checker == nil {
+				if test.Handled {
+					t.Errorf("expect %q to be handled", test.Type)
+					t.Fail()
+				}
+				return
+			}
+
+			if !test.Handled {
+				t.Errorf("expect %q NOT to be handled", test.Type)
+				t.Fail()
+			}
+		})
+	}
+
+}
+
+func TestFloat64_Values(t *testing.T) {
+	t.Parallel()
+
+	const typeName = "float"
+
+	checker := builtin.NewFloat64().Checker(typeName)
+	if checker == nil {
+		t.Errorf("expect %q to be handled", typeName)
+		t.Fail()
+	}
+
+	tests := []struct {
+		Value interface{}
+		Valid bool
+	}{
+		{uint(0), true},
+		{uint(math.MaxInt64), true},
+		{uint(math.MaxUint64), true},
+		{-1, true},
+		{-math.MaxInt64, true},
+
+		{float64(math.MinInt64), true},
+		{float64(0), true},
+		{float64(math.MaxInt64), true},
+		// we cannot just compare because of how precision works
+		{float64(math.MaxUint64 - 1024), true},
+		{float64(math.MaxUint64 + 1), true},
+
+		// json number
+		{fmt.Sprintf("%f", -math.MaxFloat64), true},
+		{"-1", true},
+		{"0", true},
+		{"1", true},
+		{fmt.Sprintf("%d", math.MaxInt64), true},
+		{fmt.Sprintf("%d", uint(math.MaxUint64)), true},
+		{fmt.Sprintf("%f", float64(math.MaxFloat64)), true},
+
+		{"string", false},
+		{[]byte("bytes"), false},
+		{-0.1, true},
+		{0.1, true},
+		{nil, false},
+	}
+
+	for i, test := range tests {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			if checker(test.Value) {
+				if !test.Valid {
+					t.Errorf("expect value to be invalid")
+					t.Fail()
+				}
+				return
+			}
+			if test.Valid {
+				t.Errorf("expect value to be valid")
+				t.Fail()
+			}
+		})
+	}
+
+}