non-existent genesis file: clarify error (#2320)

* add error message
* added a test for non-existent genesis file

Signed-off-by: Sally MacFarlane <sally.macfarlane@consensys.net>

besu/src/main/java/org/hyperledger/besu/cli/BesuCommand.java

@@ -1488,7 +1488,8 @@ public class BesuCommand implements DefaultCommandValues, Runnable {
       final GenesisConfigFile genesisConfigFile = GenesisConfigFile.fromConfig(genesisConfig());
       genesisConfigOptions = genesisConfigFile.getConfigOptions(genesisConfigOverrides);
     } catch (final Exception e) {
-      throw new IllegalStateException("Unable to read genesis file for GoQuorum options", e);
+      throw new ParameterException(
+          this.commandLine, "Unable to load genesis file. " + e.getCause());
     }
     return genesisConfigOptions;
   }

besu/src/test/java/org/hyperledger/besu/cli/BesuCommandTest.java

@@ -994,6 +994,18 @@ public class BesuCommandTest extends CommandTestAbstract {
         .startsWith("--network option and --genesis-file option can't be used at the same time.");
   }
 
+  @Test
+  public void nonExistentGenesisGivesError() throws Exception {
+    final String nonExistentGenesis = "non-existent-genesis.json";
+    parseCommand("--genesis-file", nonExistentGenesis);
+
+    Mockito.verifyZeroInteractions(mockRunnerBuilder);
+
+    assertThat(commandOutput.toString()).isEmpty();
+    assertThat(commandErrorOutput.toString()).startsWith("Unable to load genesis file");
+    assertThat(commandErrorOutput.toString()).contains(nonExistentGenesis);
+  }
+
   @Test
   public void testDnsDiscoveryUrlEthConfig() throws Exception {
     final ArgumentCaptor<EthNetworkConfig> networkArg =