SONAR-19050 Add tests to fix coverage

sonar-core/src/test/java/org/sonar/core/issue/DefaultIssueTest.java

 import org.junit.Test;
 import org.sonar.api.issue.Issue;
 import org.sonar.api.rule.RuleKey;
+import org.sonar.api.rules.RuleType;
 import org.sonar.api.utils.Duration;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.Assert.fail;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
       .setUpdateDate(new SimpleDateFormat("yyyy-MM-dd").parse("2013-08-20"))
       .setCloseDate(new SimpleDateFormat("yyyy-MM-dd").parse("2013-08-21"))
       .setSelectedAt(1400000000000L)
-      .setRuleDescriptionContextKey(TEST_CONTEXT_KEY);
+      .setRuleDescriptionContextKey(TEST_CONTEXT_KEY)
+      .setType(RuleType.BUG);
 
     assertThat((Object) issue.getLocations()).isEqualTo("loc");
     assertThat(issue.locationsChanged()).isTrue();
     assertThat(issue.closeDate()).isEqualTo(new SimpleDateFormat("yyyy-MM-dd").parse("2013-08-21"));
     assertThat(issue.selectedAt()).isEqualTo(1400000000000L);
     assertThat(issue.getRuleDescriptionContextKey()).contains(TEST_CONTEXT_KEY);
+    assertThat(issue.type()).isEqualTo(RuleType.BUG);
   }
 
   @Test
 
     assertThat(defaultIssue.isQuickFixAvailable()).isFalse();
   }
+
+  @Test
+  public void characteristic_shouldThrowIllegalStateException() {
+    DefaultIssue defaultIssue = new DefaultIssue();
+    assertThatThrownBy(() -> defaultIssue.characteristic()).isInstanceOf(IllegalStateException.class);
+  }
 }

sonar-plugin-api-impl/src/test/java/org/sonar/api/batch/sensor/issue/internal/DefaultExternalIssueTest.java

 import org.sonar.api.batch.fs.internal.TestInputFileBuilder;
 import org.sonar.api.batch.rule.Severity;
 import org.sonar.api.batch.sensor.internal.SensorStorage;
+import org.sonar.api.code.CodeCharacteristic;
 import org.sonar.api.rule.RuleKey;
 import org.sonar.api.rules.RuleType;
 
       .hasMessageContaining("Severity is mandatory");
   }
 
+  @Test
+  public void characteristic_shouldThrowIllegalStateException() {
+    SensorStorage storage = mock(SensorStorage.class);
+    DefaultExternalIssue issue = new DefaultExternalIssue(project, storage);
+    assertThatThrownBy(issue::characteristic).isInstanceOf(IllegalStateException.class);
+    assertThatThrownBy(() -> issue.characteristic(CodeCharacteristic.CLEAR)).isInstanceOf(IllegalStateException.class);
+  }
+
 }

sonar-plugin-api-impl/src/test/java/org/sonar/api/batch/sensor/rule/internal/DefaultAdHocRuleTest.java

 import org.sonar.api.batch.rule.Severity;
 import org.sonar.api.batch.sensor.internal.SensorStorage;
 import org.sonar.api.batch.sensor.rule.NewAdHocRule;
+import org.sonar.api.code.CodeCharacteristic;
 import org.sonar.api.rules.RuleType;
 
 import static org.assertj.core.api.Assertions.assertThat;
       .description("desc")
       .severity(Severity.BLOCKER)
       .type(RuleType.CODE_SMELL);
-      rule.save();
+    rule.save();
 
     assertThat(rule.engineId()).isEqualTo("engine");
     assertThat(rule.ruleId()).isEqualTo("ruleId");
       .hasMessageContaining("Type is mandatory");
   }
 
+  @Test
+  public void characteristic_shouldThrowIllegalStateException() {
+    SensorStorage storage = mock(SensorStorage.class);
+    DefaultAdHocRule rule = new DefaultAdHocRule(storage);
+    assertThatThrownBy(() -> rule.characteristic(CodeCharacteristic.CLEAR)).isInstanceOf(IllegalStateException.class);
+    assertThatThrownBy(() -> rule.characteristic()).isInstanceOf(IllegalStateException.class);
+  }
 }