Fix empty keys in EnvironmentChangedEvent on resetting the Environment (#229)

When the Environment is resetted the EnvironmentChangedEvent always
contains an empty keySet, since the live view of the cleared map was
used. This commit fixes this.

spring-cloud-context/src/test/java/org/springframework/cloud/context/environment/EnvironmentManagerTest.java

@@ -0,0 +1,45 @@
+package org.springframework.cloud.context.environment;
+
+
+import org.junit.Test;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Mockito;
+import org.springframework.context.ApplicationEvent;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.mock.env.MockEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.*;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+public class EnvironmentManagerTest {
+
+    @Test
+    public void testCorrectEvents() {
+        MockEnvironment environment = new MockEnvironment();
+        ApplicationEventPublisher publisher = mock(ApplicationEventPublisher.class);
+        EnvironmentManager environmentManager = new EnvironmentManager(environment);
+        environmentManager.setApplicationEventPublisher(publisher);
+
+        environmentManager.setProperty("foo", "bar");
+
+        assertThat(environment.getProperty("foo")).isEqualTo("bar");
+        ArgumentCaptor<ApplicationEvent> eventCaptor = ArgumentCaptor.forClass(ApplicationEvent.class);
+        verify(publisher, times(1)).publishEvent(eventCaptor.capture());
+        assertThat(eventCaptor.getValue()).isInstanceOf(EnvironmentChangeEvent.class);
+        EnvironmentChangeEvent event = (EnvironmentChangeEvent) eventCaptor.getValue();
+        assertThat(event.getKeys()).containsExactly("foo");
+
+        reset(publisher);
+
+        environmentManager.reset();
+        assertThat(environment.getProperty("foo")).isNull();
+        verify(publisher, times(1)).publishEvent(eventCaptor.capture());
+        assertThat(eventCaptor.getValue()).isInstanceOf(EnvironmentChangeEvent.class);
+        event = (EnvironmentChangeEvent) eventCaptor.getValue();
+        assertThat(event.getKeys()).containsExactly("foo");
+    }
+
+}