Fix tests

packages/plugos-silverbullet-syscall/syscall.ts

@@ -2,4 +2,14 @@ declare global {
   function syscall(name: string, ...args: any[]): Promise<any>;
 }
 
+// This is the case when running tests only, so giving it a dummy syscall function
+if (typeof self === "undefined") {
+  // @ts-ignore
+  self = {
+    syscall: (name: string, ...args: any[]) => {
+      throw new Error("Not implemented here");
+    },
+  };
+}
+
 export const syscall = self.syscall;