test(fs-test): refactor new_file_test

new_file_test now runs a kernel called open_close_file, which attempts
to open foo.txt, write to it, then closes the file, and attempts to
open it again so as to read from it. This is more of a workaround
because of the fact that we cannot read the temporary file easily,
but it should work just as well and expand the test's coverage to
"reading the contents of a file that is a temporary file on the
host filesystem".

tests/fs-test.rs

@@ -24,13 +24,10 @@ fn new_file_test() {
 		..Default::default()
 	};
 
-	let bin_path = build_hermit_bin("create_file");
+	let bin_path = build_hermit_bin("open_close_file");
 	let vm = UhyveVm::new(bin_path, params).unwrap();
-	let mut output_path = vm.get_tempdir().path().to_path_buf();
-	output_path.push("foo.txt");
 	let res = vm.run(None);
 	assert_eq!(res.code, 0);
-	verify_file_equals(&output_path, "Hello, world!");
 }
 
 #[test]

tests/test-kernels/Cargo.toml

@@ -1,7 +1,10 @@
 [package]
 name = "uhyve-test-kernels"
 version = "0.1.0"
-authors = ["Jonathan Klimt <[email protected]>"]
+authors = [
+  "Jonathan Klimt <[email protected]>",
+  'Panagiotis "Ivory" Vasilopoulos <[email protected]>',
+]
 edition = "2021"
 publish = false
 

tests/test-kernels/src/bin/open_close_file.rs

@@ -0,0 +1,20 @@
+use std::{
+	fs::{read_to_string, File},
+	io::prelude::*,
+};
+
+#[cfg(target_os = "hermit")]
+use hermit as _;
+
+fn main() {
+	println!("Hello from open_close_file!");
+
+	{
+		let mut file = File::create("/root/foo.txt").unwrap();
+		file.write_all(b"Hello, world!").unwrap();
+	}
+	{
+		let file_content = read_to_string("/root/foo.txt").unwrap();
+		assert_eq!(file_content, "Hello, world!".to_string());
+	}
+}