Fix nomulus GetEppResourceCommand (#1865)

* Fix nomulus GetEppResourceCommand

Fixes a bug in read_timestamp validation.

Fixes string representation of Collection fields in Epp Resources.

core/src/test/java/google/registry/tools/GetEppResourceCommandTest.java

@@ -0,0 +1,58 @@
+// Copyright 2022 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.tools;
+
+import static org.junit.Assert.assertThrows;
+
+import com.google.common.truth.Truth;
+import google.registry.testing.FakeClock;
+import org.joda.time.DateTime;
+import org.joda.time.DateTimeZone;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+/** Unit tests for {@link GetEppResourceCommand}. */
+public class GetEppResourceCommandTest {
+
+  private static final DateTime TEST_TIME = DateTime.now(DateTimeZone.UTC);
+
+  private final FakeClock clock = new FakeClock(TEST_TIME);
+  private GetEppResourceCommand commandUnderTest;
+
+  @BeforeEach
+  public void setup() {
+    commandUnderTest = Mockito.spy(GetEppResourceCommand.class);
+    commandUnderTest.clock = clock;
+  }
+
+  @Test
+  public void readTimestampAfterNow_noException() {
+    commandUnderTest.readTimestamp = clock.nowUtc().plusMillis(1);
+    commandUnderTest.run();
+  }
+
+  @Test
+  public void readTimestampBeforeNow_throwsException() {
+    commandUnderTest.readTimestamp = clock.nowUtc().minusMillis(1);
+    assertThrows(IllegalArgumentException.class, () -> commandUnderTest.run());
+  }
+
+  @Test
+  public void readTimestampNotProvided_setToNow_noException() {
+    commandUnderTest.run();
+    Truth.assertThat(commandUnderTest.readTimestamp).isEqualTo(clock.nowUtc());
+  }
+}