tests/alloc/gp8: allocator test using all 8-bit registers (#102)

Updates #43

tests/alloc/gp8/gp8_test.go

@@ -0,0 +1,15 @@
+package gp8
+
+import (
+	"testing"
+)
+
+//go:generate go run asm.go -out gp8.s -stubs stub.go
+
+func TestGP8(t *testing.T) {
+	const n = 19
+	expect := uint8(n * (n + 1) / 2)
+	if got := GP8(); got != expect {
+		t.Fatalf("GP8() = %d; expect %d", got, expect)
+	}
+}