added isEmpty assertion (requested at assertj#12)

src/main/java/org/assertj/db/api/AbstractColumnAssert.java

@@ -93,6 +93,12 @@ protected List<Value> getValuesList() {
     return column.getValuesList();
   }
 
+  /** {@inheritDoc} */
+  @Override
+  public C isEmpty() {
+    return hasNumberOfRows(0);
+  }
+
   /** {@inheritDoc} */
   @Override
   public C hasNumberOfRows(int expected) {

src/main/java/org/assertj/db/api/AbstractDbAssert.java

@@ -115,6 +115,12 @@ public C column(String columnName) {
     return columnPosition.getInstance(actual.getColumnsList(), actual.getColumnsNameList(), columnName, actual.getColumnLetterCase());
   }
 
+  /** {@inheritDoc} */
+  @Override
+  public A isEmpty() {
+    return hasNumberOfRows(0);
+  }
+
   /** {@inheritDoc} */
   @Override
   public A hasNumberOfRows(int expected) {

src/main/java/org/assertj/db/api/assertions/AssertOnNumberOfRows.java

@@ -22,6 +22,23 @@
  */
 public interface AssertOnNumberOfRows<T extends AssertOnNumberOfRows<T>> {
 
+  /**
+   * Verifies that the number of rows is zero.
+   * <p>
+   * Example where the assertion verifies that the table is empty :
+   * </p>
+   *
+   * <pre><code class='java'>
+   * assertThat(table).isEmpty();
+   * </code></pre>
+   *
+   * @return {@code this} assertion object.
+   * @throws AssertionError If the number of rows is different from zero.
+   * @see org.assertj.db.api.AbstractDbAssert#isEmpty()
+   * @see org.assertj.db.api.AbstractColumnAssert#isEmpty()
+   */
+  T isEmpty();
+
   /**
    * Verifies that the number of rows is equal to the number in parameter.
    * <p>

src/test/java/org/assertj/db/api/assertions/AssertOnNumberOfRows_IsEmpty_Test.java

@@ -0,0 +1,74 @@
+/**
+ * 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.
+ *
+ * Copyright 2012-2016 the original author or authors.
+ */
+package org.assertj.db.api.assertions;
+
+import org.assertj.core.api.Assertions;
+import org.assertj.db.api.TableAssert;
+import org.assertj.db.api.TableColumnAssert;
+import org.assertj.db.common.AbstractTest;
+import org.assertj.db.type.Request;
+import org.assertj.db.type.Table;
+import org.junit.Test;
+
+import static org.assertj.db.api.Assertions.assertThat;
+import static org.junit.Assert.fail;
+
+/**
+ * Tests on {@link org.assertj.db.api.assertions.AssertOnNumberOfRows} class :
+ * {@link AssertOnNumberOfRows#isEmpty()} method.
+ */
+public class AssertOnNumberOfRows_IsEmpty_Test extends AbstractTest {
+
+  /**
+   * This method tests the {@code isEmpty} assertion method.
+   */
+  @Test
+  public void test_is_empty() {
+    update("delete from test");
+    Table table = new Table(source, "test");
+    TableAssert tableAssert = assertThat(table);
+    TableAssert tableAssert2 = tableAssert.isEmpty();
+    Assertions.assertThat(tableAssert).isSameAs(tableAssert2);
+    TableColumnAssert tableColumnAssert = assertThat(table).column();
+    TableColumnAssert tableColumnAssert2 = tableColumnAssert.isEmpty();
+    Assertions.assertThat(tableColumnAssert).isSameAs(tableColumnAssert2);
+  }
+
+  /**
+   * This method should fail because table is not empty.
+   */
+  @Test
+  public void should_fail_because_table_is_not_empty() {
+    Request request = new Request(source, "select * from actor");
+    try {
+      assertThat(request).isEmpty();
+      fail("An exception must be raised");
+    } catch (AssertionError e) {
+      Assertions.assertThat(e.getMessage()).isEqualTo(String.format("['select * from actor' request] %n"
+                                                      + "Expecting size (number of rows) to be equal to :%n"
+                                                      + "   <0>%n"
+                                                      + "but was:%n"
+                                                      + "   <3>"));
+    }
+    try {
+      assertThat(request).column().isEmpty();
+      fail("An exception must be raised");
+    } catch (AssertionError e) {
+      Assertions.assertThat(e.getMessage()).isEqualTo(String.format("[Column at index 0 (column name : ID) of 'select * from actor' request] %n"
+                                                      + "Expecting size (number of rows) to be equal to :%n"
+                                                      + "   <0>%n"
+                                                      + "but was:%n"
+                                                      + "   <3>"));
+    }
+  }
+}