test: add unit test for p1, based on manual calculations

internal/2015/DaySeven/code_test.go

@@ -0,0 +1,23 @@
+package dayseven
+
+import "testing"
+
+var testInput = []string{
+	"123 -> x",
+	"456 -> y",
+	"x AND y -> d",
+	"x OR y -> e",
+	"x LSHIFT 2 -> f",
+	"y RSHIFT 2 -> g",
+	"NOT x -> h",
+	"NOT y -> i",
+	"d -> a",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 72
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}