diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..b9ef394
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,2 @@
+test:
+	go test
diff --git a/util.go b/util.go
index ac13284..d078a90 100644
--- a/util.go
+++ b/util.go
@@ -70,16 +70,22 @@ func CopyFile(src, dst string) (err error) {
 	return
 }
 
-func TimeFromUnixMilli(ms int64) time.Time {
-	const millisInSecond = 1000
-	const nsInSecond = 1000000
-	return time.Unix(ms/int64(millisInSecond), (ms%int64(millisInSecond))*int64(nsInSecond))
+const milliInSecond int64 = 1000
+const microInSecond int64 = 1000000
+const nsInSecond int64 = 1000000000
+
+func TimeFromUnixMilli(input int64) time.Time {
+	var wholeSeconds int64 = input / milliInSecond
+	var remainderMillis int64 = input - (wholeSeconds * milliInSecond)
+	var remainderNano int64 = remainderMillis * 1000000
+	return time.Unix(wholeSeconds, remainderNano)
 }
 
-func TimeFromUnixMicro(ms int64) time.Time {
-	const microInSecond = 1000000
-	const nsInSecond = 1000000
-	return time.Unix(ms/int64(microInSecond), (ms%int64(microInSecond))*int64(nsInSecond))
+func TimeFromUnixMicro(input int64) time.Time {
+	var wholeSeconds int64 = input / microInSecond
+	var remainderMicros int64 = input - (wholeSeconds * microInSecond)
+	var remainderNano int64 = remainderMicros * 1000
+	return time.Unix(wholeSeconds, remainderNano)
 }
 
 func TimeFromWebKit(input int64) time.Time {
diff --git a/util_test.go b/util_test.go
new file mode 100644
index 0000000..1cba94f
--- /dev/null
+++ b/util_test.go
@@ -0,0 +1,51 @@
+package goutil
+
+import (
+	"testing"
+	"time"
+)
+
+func TestFromUnixMilli(t *testing.T) {
+	ms := 1542810446506
+	ts := TimeFromUnixMilli(int64(ms))
+	if ts.UTC().String() != "2018-11-21 14:27:26.506 +0000 UTC" {
+		t.Errorf("Expected time to be '2018-11-21 14:27:26.506 +0000 UTC' got '%s'", ts.UTC().String())
+	}
+}
+
+func TestFromUnixMicro(t *testing.T) {
+	ms := 1542810446506000
+	ts := TimeFromUnixMicro(int64(ms))
+	if ts.UTC().String() != "2018-11-21 14:27:26.506 +0000 UTC" {
+		t.Errorf("Expected time to be '2018-11-21 14:27:26.506 +0000 UTC' got '%s'", ts.UTC().String())
+	}
+}
+
+func TestFromWebkit(t *testing.T) {
+	var wk int64 = 13245202142853170
+	ts := TimeFromWebKit(wk)
+	expected := "2020-09-21 22:49:02.85317 +0000 UTC"
+	if ts.UTC().String() != expected {
+		t.Errorf("Expected time to be '%s' got '%s'", expected, ts.UTC().String())
+	}
+}
+
+func TestNowUnixMicro(t *testing.T) {
+	now := time.Now()
+	nownano := now.UnixNano()
+	nowmicro := nownano / 1000
+	ts := TimeFromUnixMicro(nowmicro)
+	if ts.UTC().String() != now.UTC().String() {
+		t.Errorf("Expected '%s' got '%s'", now.UTC().String(), ts.UTC().String())
+	}
+}
+
+func TestNowUnixMilli(t *testing.T) {
+	now := time.Now()
+	nownano := now.UnixNano()
+	nowmilli := nownano / 1000000
+	ts := TimeFromUnixMilli(nowmilli)
+	if ts.UTC().Format(time.StampMilli) != now.UTC().Format(time.StampMilli) {
+		t.Errorf("Expected '%s' got '%s'", now.UTC().String(), ts.UTC().String())
+	}
+}