test: add client -> example.com test

This commit adds a unit test that uses the client test binary to
connect to https://example.com, validating the presented certificate
chain using the system default CA bundle. We do this with `NO_ECHO=1` to
avoid trying to write a non-HTTP request and asserting on an echoed
response.

rustls-libssl/tests/runner.rs

@@ -88,6 +88,29 @@ fn client() {
     assert_eq!(openssl_secure_output, rustls_secure_output);
 }
 
+#[test]
+#[ignore]
+fn client_real_world() {
+    let openssl_output = Command::new("target/client")
+        .env("LD_LIBRARY_PATH", "")
+        .env("NO_ECHO", "1")
+        .args(&["example.com", "443", "default"])
+        .stdout(Stdio::piped())
+        .output()
+        .map(print_output)
+        .unwrap();
+
+    let rustls_output = Command::new("target/client")
+        .env("NO_ECHO", "1")
+        .args(&["example.com", "443", "default"])
+        .stdout(Stdio::piped())
+        .output()
+        .map(print_output)
+        .unwrap();
+
+    assert_eq!(openssl_output, rustls_output);
+}
+
 #[test]
 #[ignore]
 fn constants() {