feat: solve day nine part 1

cmd/09/main_test.go

@@ -0,0 +1,27 @@
+package main_test
+
+import (
+	"testing"
+
+	solution "github.com/StevanFreeborn/advent-of-code-2025/cmd/09"
+)
+
+func TestSolvePartOneWithExampleInput(t *testing.T) {
+	expected := 50
+
+	result := solution.SolvePartOne("EXAMPLE.txt")
+
+	if result != expected {
+		t.Errorf("got %d but wanted %d", result, expected)
+	}
+}
+
+func TestSolvePartOneWithInput(t *testing.T) {
+	expected := 4_758_121_828
+
+	result := solution.SolvePartOne("INPUT.txt")
+
+	if result != expected {
+		t.Errorf("got %d but wanted %d", result, expected)
+	}
+}