tests: respect naming conventions and improve nesting of some test suites

Change-Id: I255c27b552b32570871a9d5f8bda814ba8723c80
Refs: #2497
diff --git a/tests/unit-tests/security/digest-sha256.t.cpp b/tests/unit-tests/security/digest-sha256.t.cpp
index 67b6730..cbac8e2 100644
--- a/tests/unit-tests/security/digest-sha256.t.cpp
+++ b/tests/unit-tests/security/digest-sha256.t.cpp
@@ -30,24 +30,20 @@
 namespace ndn {
 namespace tests {
 
-BOOST_FIXTURE_TEST_SUITE(SecurityDigestSha256, IdentityManagementFixture)
-
-std::string SHA256_RESULT("a883dafc480d466ee04e0d6da986bd78eb1fdd2178d04693723da3a8f95d42f4");
+BOOST_AUTO_TEST_SUITE(Security)
+BOOST_FIXTURE_TEST_SUITE(TestDigestSha256, IdentityManagementFixture)
 
 BOOST_AUTO_TEST_CASE(Sha256)
 {
-  using namespace CryptoPP;
-
   char content[6] = "1234\n";
   ConstBufferPtr buf = crypto::computeSha256Digest(reinterpret_cast<uint8_t*>(content), 5);
 
-  BOOST_CHECK_EQUAL(SHA256_RESULT, toHex(buf->buf(), buf->size(), false));
+  BOOST_CHECK_EQUAL(toHex(buf->buf(), buf->size(), false),
+                    "a883dafc480d466ee04e0d6da986bd78eb1fdd2178d04693723da3a8f95d42f4");
 }
 
 BOOST_AUTO_TEST_CASE(DataSignature)
 {
-  using namespace CryptoPP;
-
   Name name("/TestSignatureSha/Basic");
   Data testData(name);
   char content[5] = "1234";
@@ -79,7 +75,8 @@
   BOOST_CHECK(Validator::verifySignature(testInterest, sig));
 }
 
-BOOST_AUTO_TEST_SUITE_END()
+BOOST_AUTO_TEST_SUITE_END() // TestDigestSha256
+BOOST_AUTO_TEST_SUITE_END() // Security
 
 } // namespace tests
 } // namespace ndn