Merge pull request #946 from hcoles/feature/mutate_to_empty_stream

Mutate stream returns to Stream.empty

README.md

@@ -11,6 +11,7 @@ Read all about it at http://pitest.org
 ### 1.7.2 (unreleased)
 
 * #943 Change default mutators - replace negate conditional with remove conditional
+* #946 Mutate stream returns to empty stream instead of null
 
 ### 1.7.1
 

pitest-entry/src/main/java/org/pitest/mutationtest/build/intercept/equivalent/EquivalentReturnMutationFilter.java

@@ -266,6 +266,7 @@ public boolean test(MutationDetails a) {
         return returnsZeroValue(method, mutatedInstruction)
             || returnsEmptyString(method, mutatedInstruction)
             || returns(method, mutatedInstruction, "java/util/Optional","empty")
+            || returns(method, mutatedInstruction, "java/util/stream/Stream","empty")
             || returns(method, mutatedInstruction, "java/util/Collections","emptyList")
             || returns(method, mutatedInstruction, "java/util/Collections","emptySet")
             || returns(method, mutatedInstruction, "java/util/List","of")

pitest-entry/src/main/resources/META-INF/services/org.pitest.mutationtest.build.MutationInterceptorFactory

@@ -17,6 +17,5 @@ org.pitest.mutationtest.build.intercept.kotlin.KotlinFilterFactory
 org.pitest.mutationtest.filter.LimitNumberOfMutationsPerClassFilterFactory
 org.pitest.mutationtest.build.intercept.equivalent.EqualsPerformanceShortcutFilterFactory
 org.pitest.mutationtest.build.intercept.equivalent.EquivalentReturnMutationFilter
-org.pitest.mutationtest.build.intercept.equivalent.NullFlatMapFilterFactory
 
 org.pitest.plugin.export.MutantExportFactory

pitest-entry/src/test/java/org/pitest/mutationtest/build/MutationDiscoveryTest.java

@@ -212,16 +212,6 @@ public void filtersEquivalentReturnValsMutants() {
     assertThat(actual).isEmpty();
   }
 
-  @Test
-  public void filtersEquivalentNullStreamMutantsUsedInFlatMapCalls() {
-    final Collection<MutationDetails> actual = findMutants(HasPrivateStreamMethodUsedOnlyInSingleFlatMap.class);
-
-    this.data.setFeatures(Collections.singletonList("-FNULLSTREAM"));
-    final Collection<MutationDetails> actualWithoutFilter = findMutants(HasPrivateStreamMethodUsedOnlyInSingleFlatMap.class);
-
-    assertThat(actual.size()).isLessThan(actualWithoutFilter.size());
-  }
-
   @Test
   public void filterMutantsInJavaRecords() {
     this.data.setDetectInlinedCode(true);

pitest-entry/src/test/java/org/pitest/mutationtest/build/intercept/equivalent/EquivalentReturnMutationFilterTest.java

@@ -13,6 +13,7 @@
 import java.util.List;
 import java.util.Optional;
 import java.util.Set;
+import java.util.stream.Stream;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.pitest.mutationtest.engine.gregor.mutators.returns.BooleanFalseReturnValsMutator.FALSE_RETURNS;
@@ -157,6 +158,11 @@ public void filtersEquivalentSetMutants() {
   public void filtersEquivalentOptionalMutants() {
     verifier.assertFiltersNMutationFromClass(1, AlreadyReturnsEmptyOptional.class);
   }
+
+  @Test
+  public void filtersEquivalentStreamMutants() {
+    verifier.assertFiltersNMutationFromClass(1, AlreadyReturnsEmptyStream.class);
+  }
 }
 
 class Widget{}
@@ -334,3 +340,9 @@ public Optional<String> a() {
     return Optional.empty();
   }
 }
+
+class AlreadyReturnsEmptyStream {
+  public Stream<String> a() {
+    return Stream.empty();
+  }
+}