Fix tests in --disable-postgres build (#4626)

Resolves #4625 and #4614.

This change fixes the tests in the `--disable-postgres` build by
disabling parallel ledger close tests when postgres is disabled. This is
necessary because parallel ledger close requires postgres.

As part of this, I also removed the
`TESTDB_BUCKET_DB_PERSISTENT_POSTGRES` test mode, as it's made redundant
by the `TESTDB_POSTGRESQL` mode.

# Checklist
- [x] Reviewed the
[contributing](https://github.com/stellar/stellar-core/blob/master/CONTRIBUTING.md#submitting-changes)
document
- [x] Rebased on top of master (no merge commits)
- [x] Ran `clang-format` v8.0.0 (via `make format` or the Visual Studio
extension)
- [x] Compiles
- [x] Ran all tests
- [ ] If change impacts performance, include supporting evidence per the
[performance
document](https://github.com/stellar/stellar-core/blob/master/performance-eval/performance-eval.md)

Author: SirTyson

src/herder/test/HerderTests.cpp

@@ -3222,20 +3222,23 @@ TEST_CASE("overlay parallel processing")
                 return cfg;
             });
     }
+
+// Background ledger close requires postgres
+#ifdef USE_POSTGRES
     SECTION("background ledger close")
     {
         // Set threshold to 1 so all have to vote
         simulation =
             Topologies::core(4, 1, Simulation::OVER_TCP, networkID, [](int i) {
-                auto cfg = getTestConfig(
-                    i, Config::TESTDB_BUCKET_DB_PERSISTENT_POSTGRES);
+                auto cfg = getTestConfig(i, Config::TESTDB_POSTGRESQL);
                 cfg.TESTING_UPGRADE_MAX_TX_SET_SIZE = 100;
                 cfg.EXPERIMENTAL_PARALLEL_LEDGER_CLOSE = true;
                 cfg.ARTIFICIALLY_DELAY_LEDGER_CLOSE_FOR_TESTING =
                     std::chrono::milliseconds(500);
                 return cfg;
             });
     }
+#endif
 
     simulation->startAllNodes();
     auto nodes = simulation->getNodes();
@@ -3526,10 +3529,16 @@ herderExternalizesValuesWithProtocol(uint32_t version,
     auto networkID = sha256(getTestConfig().NETWORK_PASSPHRASE);
     auto simulation = std::make_shared<Simulation>(
         Simulation::OVER_LOOPBACK, networkID, [&](int i) {
-            auto cfg = getTestConfig(
-                i, parallelLedgerClose
-                       ? Config::TESTDB_BUCKET_DB_PERSISTENT_POSTGRES
-                       : Config::TESTDB_BUCKET_DB_PERSISTENT);
+            Config::TestDbMode dbMode = Config::TESTDB_BUCKET_DB_PERSISTENT;
+            if (parallelLedgerClose)
+            {
+#ifdef USE_POSTGRES
+                dbMode = Config::TESTDB_POSTGRESQL;
+#else
+                FAIL("Parallel ledger close requires postgres");
+#endif
+            }
+            auto cfg = getTestConfig(i, dbMode);
             cfg.TESTING_UPGRADE_LEDGER_PROTOCOL_VERSION = version;
             if (parallelLedgerClose)
             {

src/main/Config.h

@@ -163,7 +163,6 @@ class Config : public std::enable_shared_from_this<Config>
 #endif
         TESTDB_BUCKET_DB_VOLATILE,
         TESTDB_BUCKET_DB_PERSISTENT,
-        TESTDB_BUCKET_DB_PERSISTENT_POSTGRES,
         TESTDB_MODES
     };
 

src/test/test.cpp

@@ -291,10 +291,6 @@ getTestConfig(int instanceNumber, Config::TestDbMode mode)
             thisConfig.DISABLE_XDR_FSYNC = false;
             break;
 #ifdef USE_POSTGRES
-        case Config::TESTDB_BUCKET_DB_PERSISTENT_POSTGRES:
-            dbname << "postgresql://dbname=test" << instanceNumber;
-            thisConfig.DISABLE_XDR_FSYNC = false;
-            break;
         case Config::TESTDB_POSTGRESQL:
             dbname << "postgresql://dbname=test" << instanceNumber;
             thisConfig.DISABLE_XDR_FSYNC = false;