tests: add LE chain test to verification_real_world

In particular this testcase ensures that we can validate a chain from
EE->intermediate->trust anchor for a chain where one or more
certificates (in this case, the intermediate) are missing an authority
information access (AIA) extension that specifies an OCSP access method
and URI.

src/tests/verification_real_world/mod.rs

@@ -77,6 +77,14 @@ const VALID_UNRELATED_CHAIN: &[&[u8]] = &[
     include_bytes!("agilebits_com_valid_4.crt"),
 ];
 
+const LETSENCRYPT_ORG: &str = "letsencrypt.org";
+
+const VALID_LETSENCRYPT_ORG_CHAIN: &[&[u8]] = &[
+    include_bytes!("letsencrypt_org_valid_1.crt"),
+    include_bytes!("letsencrypt_org_valid_2.crt"),
+    include_bytes!("letsencrypt_org_valid_3.crt"),
+];
+
 macro_rules! real_world_test_cases {
     { $( $name:ident => $test_case:expr ),+ , } => {
         real_world_test_cases!(@ $($name => $test_case),+,);
@@ -202,6 +210,13 @@ real_world_test_cases! {
         expected_result: Err(TlsError::InvalidCertificate(CertificateError::NotValidForName)),
         other_error: no_error!(),
     },
+    letsencrypt => TestCase {
+        reference_id: LETSENCRYPT_ORG,
+        chain: VALID_LETSENCRYPT_ORG_CHAIN,
+        stapled_ocsp: None,
+        expected_result: Ok(()),
+        other_error: no_error!(),
+    },
 
     // OCSP stapling works.
     //