diff --git a/day02/main.go b/day02/main.go
index 7f2f2b2..f9759c2 100644
--- a/day02/main.go
+++ b/day02/main.go
@@ -2,24 +2,39 @@ package main
 
 import (
 	"bufio"
-	"bytes"
 	_ "embed"
 	"fmt"
+	"os"
 	"strconv"
 	"strings"
+
+	aoc "go.sour.is/advent-of-code-2023"
 )
 
-//go:embed input.txt
-var input []byte
+func main() {
+	result, err := aoc.Runner(run)
+	if err != nil {
+		aoc.Log("ERR", err)
+		os.Exit(1)
+	}
+
+	aoc.Log(result)
+}
+
+type result struct {
+	sum      int
+	powerSum int
+}
+
+func (r result) String() string {
+	return fmt.Sprintln("result pt1:", r.sum, "\nresult pt2:", r.powerSum)
+}
 
 type gameResult struct {
 	red, green, blue int
 }
 
-func main() {
-	buf := bytes.NewReader(input)
-	scan := bufio.NewScanner(buf)
-
+func run(scan *bufio.Scanner) (*result, error) {
 	// only 12 red cubes, 13 green cubes, and 14 blue cubes
 	maxCounts := gameResult{
 		red:   12,
@@ -62,8 +77,8 @@ func main() {
 		}
 	}
 
-	fmt.Println(games)
-	fmt.Println(len(games))
+	aoc.Log(games)
+	aoc.Log(len(games))
 
 	sum := 0
 	powerSum := 0
@@ -81,24 +96,24 @@ func main() {
 			mins.blue = max(mins.blue, round.blue)
 
 			if maxCounts.red < round.red {
-				fmt.Println("game", i, round, "too many red", round.red)
+				aoc.Log("game", i, round, "too many red", round.red)
 				ok = false
 			} else if maxCounts.blue < round.blue {
-				fmt.Println("game", i, round, "too many blue", round.blue)
+				aoc.Log("game", i, round, "too many blue", round.blue)
 				ok = false
 			} else if maxCounts.green < round.green {
-				fmt.Println("game", i, round, "too many green", round.green)
+				aoc.Log("game", i, round, "too many green", round.green)
 				ok = false
 			}
-			fmt.Println("game", i, round, ok)
+			aoc.Log("game", i, round, ok)
 		}
 		if ok {
 			sum += i
-			fmt.Println("game", i, "passes", sum)
+			aoc.Log("game", i, "passes", sum)
 		}
-		power := mins.red*mins.blue*mins.green
-		fmt.Println("game", i, "mins", mins, power)
+		power := mins.red * mins.blue * mins.green
+		aoc.Log("game", i, "mins", mins, power)
 		powerSum += power
 	}
-	fmt.Println("sum", sum, "power", powerSum)
+	return &result{sum, powerSum}, nil
 }
diff --git a/day02/main_test.go b/day02/main_test.go
new file mode 100644
index 0000000..23215eb
--- /dev/null
+++ b/day02/main_test.go
@@ -0,0 +1,41 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"testing"
+
+	_ "embed"
+
+	"github.com/matryer/is"
+)
+
+//go:embed example.txt
+var example []byte
+
+//go:embed input.txt
+var input []byte
+
+func TestExample(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(example))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.sum, 8)
+	is.Equal(result.powerSum, 2286)
+}
+
+func TestSolution(t *testing.T) {
+	is := is.New(t)
+	scan := bufio.NewScanner(bytes.NewReader(input))
+
+	result, err := run(scan)
+	is.NoErr(err)
+
+	t.Log(result)
+	is.Equal(result.sum, 2317)
+	is.Equal(result.powerSum, 74804)
+}
diff --git a/tools.go b/tools.go
index a78e990..05f87aa 100644
--- a/tools.go
+++ b/tools.go
@@ -4,22 +4,33 @@ import (
 	"bufio"
 	"fmt"
 	"os"
+	"strings"
 )
 
 func Runner[R any, F func(*bufio.Scanner) (R, error)](run F) (R, error) {
 	if len(os.Args) != 2 {
-		fmt.Fprintln(os.Stderr, "Usage:", os.Args[0] , "FILE")
+		Log("Usage:", os.Args[0], "FILE")
+		os.Exit(22)
 	}
 
 	input, err := os.Open(os.Args[1])
 	if err != nil {
-		fmt.Fprintln(os.Stderr, err)
+		Log(err)
+		os.Exit(1)
 	}
 
 	scan := bufio.NewScanner(input)
 	return run(scan)
 }
 
+func Log(v ...any) { fmt.Fprintln(os.Stderr, v...) }
+func Logf(format string, v ...any) {
+	if !strings.HasSuffix(format, "\n") {
+		format += "\n"
+	}
+	fmt.Fprintf(os.Stderr, format, v...)
+}
+
 func Reverse[T any](arr []T) []T {
 	for i := 0; i < len(arr)/2; i++ {
 		arr[i], arr[len(arr)-i-1] = arr[len(arr)-i-1], arr[i]
@@ -27,9 +38,16 @@ func Reverse[T any](arr []T) []T {
 	return arr
 }
 
+type integer interface {
+	int | int8 | int16 | int32 | int64 | uint | uint8 | uint16 | uint32 | uint64
+}
+// type float interface {
+// 	complex64 | complex128 | float32 | float64
+// }
+// type number interface{ integer | float }
 
 // greatest common divisor (GCD) via Euclidean algorithm
-func GCD(a, b uint64) uint64 {
+func GCD[T integer](a, b T) T {
 	for b != 0 {
 		t := b
 		b = a % b
@@ -39,7 +57,7 @@ func GCD(a, b uint64) uint64 {
 }
 
 // find Least Common Multiple (LCM) via GCD
-func LCM(integers ...uint64) uint64 {
+func LCM[T integer](integers ...T) T {
 	if len(integers) == 0 {
 		return 0
 	}