slowCheck: handle exceptions from generators

slowCheck/src/slowCheck/GeneratorException.java

@@ -0,0 +1,11 @@
+package slowCheck;
+
+/**
+ * @author peter
+ */
+public class GeneratorException extends RuntimeException {
+
+  GeneratorException(long seed, Throwable cause) {
+    super("Exception while generating data, seed=" + seed, cause);
+  }
+}

slowCheck/src/slowCheck/PropertyChecker.java

@@ -79,7 +79,13 @@ public class PropertyChecker<T> {
   private CounterExampleImpl<T> findCounterExample(int sizeHint) {
     for (int i = 0; i < 100; i++) {
       StructureNode node = new StructureNode();
-      T value = generator.generateUnstructured(new GenerativeDataStructure(random, node, sizeHint));
+      T value;
+      try {
+        value = generator.generateUnstructured(new GenerativeDataStructure(random, node, sizeHint));
+      }
+      catch (Throwable e) {
+        throw new GeneratorException(seed, e);
+      }
       if (!generatedHashes.add(node.hashCode())) continue;
       
       return CounterExampleImpl.checkProperty(property, value, node);
@@ -92,12 +98,18 @@ public class PropertyChecker<T> {
     private CounterExampleImpl<T> minimized;
     private int totalSteps;
     private int sizeHint;
+    private Throwable stoppingReason;
 
     PropertyFailureImpl(@NotNull CounterExampleImpl<T> initial, int sizeHint) {
       this.initial = initial;
       this.minimized = initial;
       this.sizeHint = sizeHint;
-      shrink();
+      try {
+        shrink();
+      }
+      catch (Throwable e) {
+        stoppingReason = e;
+      }
     }
 
     @NotNull
@@ -112,6 +124,12 @@ public class PropertyChecker<T> {
       return minimized;
     }
 
+    @Nullable
+    @Override
+    public Throwable getStoppingReason() {
+      return stoppingReason;
+    }
+
     @Override
     public int getTotalMinimizationStepCount() {
       return totalSteps;

slowCheck/src/slowCheck/PropertyFailure.java

@@ -12,6 +12,9 @@ public interface PropertyFailure<T> {
 
   @NotNull
   CounterExample<T> getMinimalCounterexample();
+
+  @Nullable
+  Throwable getStoppingReason();
   
   int getTotalMinimizationStepCount();
 

slowCheck/test/slowCheck/ExceptionTest.java

@@ -1,6 +1,8 @@
 package slowCheck;
 
+import static slowCheck.Generator.from;
 import static slowCheck.Generator.integers;
+import static slowCheck.Generator.listsOf;
 
 /**
  * @author peter
@@ -48,4 +50,38 @@ public class ExceptionTest extends PropertyCheckerTestCase {
     }
   }
 
+  public void testExceptionWhileGeneratingValue() {
+    try {
+      PropertyChecker.forAll(ourTestSettings, from(data -> {
+        throw new AssertionError("fail");
+      }), i -> true);
+      fail();
+    }
+    catch (GeneratorException ignore) {
+    }
+  }
+
+  public void testExceptionWhileShrinkingValue() {
+    try {
+      PropertyChecker.forAll(ourTestSettings, listsOf(integers()).suchThat(l -> {
+        if (l.size() == 1 && l.get(0) == 0) throw new RuntimeException("my exception");
+        return true;
+      }), l -> l.stream().allMatch(i -> i > 0));
+      fail();
+    }
+    catch (PropertyFalsified e) {
+      assertEquals("my exception", e.getFailure().getStoppingReason().getMessage());
+    }
+  }
+
+  public void testUnsatisfiableSuchThat() {
+    try {
+      PropertyChecker.forAll(integers(-1, 1).suchThat(i -> i > 2), i -> i == 0);
+      fail();
+    }
+    catch (GeneratorException e) {
+      assertTrue(e.getCause() instanceof CannotSatisfyCondition);
+    }
+  }
+
 }

slowCheck/test/slowCheck/GeneratorTest.java

@@ -75,15 +75,6 @@ public class GeneratorTest extends PropertyCheckerTestCase {
     PropertyChecker.forAll(integers().suchThat(i -> i < 0), i -> i < 0);
   }
 
-  public void testUnsatisfiableSuchThat() {
-    try {
-      PropertyChecker.forAll(integers(-1, 1).suchThat(i -> i > 2), i -> i == 0);
-      fail();
-    }
-    catch (CannotSatisfyCondition ignored) {
-    }
-  }
-
   public void testStringOfStringChecksAllChars() {
     checkFalsified(stringsOf("abc "),
                    s -> !s.contains(" "),