diff --git a/.gitea/workflows/fib-test.yaml b/.gitea/workflows/fib-test.yaml
index a4e22e4..c27c82d 100644
--- a/.gitea/workflows/fib-test.yaml
+++ b/.gitea/workflows/fib-test.yaml
@@ -21,6 +21,7 @@ jobs:
         with:
           go-version: '1.24.4'
           check-latest: true
-      - name: Build the fib app
+      - name: Test build
         run: go build
-      - run: echo "🍏 This job's status is ${{ job.status }}."
+      - name: Test functions module
+	run: go test ./functions -v
diff --git a/.gitignore b/.gitignore
index 626e811..89b7ade 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,7 @@
 # Ignore everything
 *
 
+.env
 # But not these files...
 !/.gitignore
 
diff --git a/functions/fibonacci.go b/functions/fibonacci.go
index 3e1adf2..0a06a25 100644
--- a/functions/fibonacci.go
+++ b/functions/fibonacci.go
@@ -1,9 +1,18 @@
 package functions
 
-func MyFibonacci(count int) (fibonaccivalue int) {
+import(
+	"errors"
+	"fmt"
+)
+
+func MyFibonacci(count int) (fibonaccivalue int, error error) {
 	fibonaccivalue = 1
+	error = nil
 	var prev_fibonacci int = 0
 
+	if count < 1 {
+		return -1, errors.New(fmt.Sprintf("%d is not a positive integer.",count))
+	}
 	for i := 1; i < count; i++ {
 		fibonaccivalue += prev_fibonacci
 		prev_fibonacci = fibonaccivalue - prev_fibonacci
diff --git a/functions/flagcheck.go b/functions/flagcheck.go
new file mode 100644
index 0000000..97a0be4
--- /dev/null
+++ b/functions/flagcheck.go
@@ -0,0 +1,15 @@
+package functions
+
+import (
+	"flag"
+)
+
+func FlagSet(name string) (found bool) {
+	found = false
+	flag.Visit(func (f *flag.Flag) {
+		if f.Name == name {
+			found = true
+		}
+	})
+	return 
+}
diff --git a/functions/functions_test.go b/functions/functions_test.go
new file mode 100644
index 0000000..4a7d96c
--- /dev/null
+++ b/functions/functions_test.go
@@ -0,0 +1,52 @@
+package functions
+
+import (
+	"testing"
+	"fmt"
+)
+
+// Test fibonacci function
+
+func TestFibonacci(t *testing.T) {
+	var sequence = [4]int{1, 3, 5, 9}
+	var values = [4]int{1, 2, 5, 34}
+	for i := 0; i < len(sequence); i++ {
+		var seq, want = sequence[i], values[i]
+		outcome, error := MyFibonacci(seq)
+		if error != nil {
+			t.Errorf("Error trying to Fibonacci %d: %s", seq, error)
+		}
+		if outcome != want {
+			t.Errorf("Invalid outcome: Fibonacci sequence %d should be %d, got %d",
+				seq, want, outcome)
+		}
+	}
+}
+
+func TestFibBadNumber(t *testing.T) {
+	outcome,error := MyFibonacci(-4)
+	if error == nil {
+		t.Errorf("This should be an error, not a %d",outcome)
+	}
+}
+
+func TestSums(t *testing.T) {
+	var tests = []struct{
+		a, b int
+		want int
+	} {
+		{1, 2, 3},
+		{5, 3, 8},
+		{9, 4, 13},
+	}
+
+	for _, tt := range tests {
+		testname := fmt.Sprintf("%d+%d",tt.a, tt.b)
+		t.Run(testname, func(t *testing.T) {
+			result := sum(tt.a, tt.b)
+			if result != tt.want {
+				t.Errorf("Expected %d, got %d", tt.want,result)
+			}
+		})
+	}
+}
diff --git a/functions/http.go b/functions/http.go
index 31cf310..05096c7 100644
--- a/functions/http.go
+++ b/functions/http.go
@@ -46,8 +46,14 @@ func HttFibonacci(w http.ResponseWriter, request *http.Request) {
 	} else {
 		fmt.Printf("Received request for Fibonacci Sequence Number %d\n",
 			seq)
+		value, error := MyFibonacci(seq)
+		if error != nil {
+			fmt.Printf("Error trying to Fibonacci %d: %s", seq, error)
+			fmt.Fprintf(w, "Error trying to Fibonacci %d: %s", seq, error)
+		} else {
 		fmt.Fprintf(w, "Fibonacci sequence index [%d]: %d\n",
-			seq, MyFibonacci(seq))
+			seq, value)
+		}
 	}
 }
 
diff --git a/main.go b/main.go
index 1cb4b34..d787c2b 100644
--- a/main.go
+++ b/main.go
@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"os"
 	"strconv"
+        "flag"
 
 	"github.com/joho/godotenv"
 
@@ -15,7 +16,7 @@ func main() {
 	var port_number int = 8098 // hard default
 	var error error
 	var bind_socket string
-	fmt.Println("Hello, world. I'm teaching myself Go.")
+	var seq, port int
 
 	error = godotenv.Load() // Load .env file
 	if error != nil {
@@ -23,16 +24,7 @@ func main() {
 	}
 	port_arg := os.Getenv("FIB_PORT")
 	if port_arg != "" {
-		fmt.Printf("Loaded port value '%s' from environment.\n",
-			port_arg)
-	}
-	if len(os.Args) > 1 { // commandline overrules env
-		port_arg = os.Args[1]
-		fmt.Printf("Loading port value '%s' from command line.\n",
-			port_arg)
-	}
-
-	if port_arg != "" {
+		fmt.Printf("Loaded port value '%s' from environment.\n",port_arg)
 		port_number, error = strconv.Atoi(port_arg)
 		if error != nil {
 			fmt.Printf("I had an error trying to parse '%s' into a number: %s\n",
@@ -41,9 +33,28 @@ func main() {
 			os.Exit(0)
 		}
 	}
-	bind_socket = fmt.Sprintf(":%d", port_number)
-	http.HandleFunc("/fibonacci", functions.HttFibonacci)
-	http.HandleFunc("/sum", functions.HttSum)
-	fmt.Printf("Listening on port %d...\n", port_number)
-	http.ListenAndServe(bind_socket, nil)
+	flag.IntVar(&port, "port", 8098, 
+		fmt.Sprintf("Port number to bind to, default %d", port_number))
+	flag.IntVar(&seq, "number", 0, 
+		"Fibonacci sequence value to calculate")
+	flag.Parse()
+
+	if functions.FlagSet("port") { // Command line overrides env
+		port_number = port
+	}
+
+	if !functions.FlagSet("number") {
+		fmt.Printf("Listening on port %d...\n", port_number)
+		bind_socket = fmt.Sprintf(":%d", port_number)
+		http.HandleFunc("/fibonacci", functions.HttFibonacci)
+		http.HandleFunc("/sum", functions.HttSum)
+		http.ListenAndServe(bind_socket, nil)
+	} else {
+		value, error := functions.MyFibonacci(seq)
+		if error != nil {
+			fmt.Printf("Failed to Fibonacci %d: %s", seq, error)
+		} else {
+			fmt.Printf("%d", value)
+		}
+	}
 }