feat: Use factory method when constructor fails

When a constructor throws an exception we will
try a factory method instead of directly failing.
Only if no factory method exists will the call fail.

Refs: JF-63

Author: akutschera

src/main/java/com/github/nylle/javafixture/InstanceFactory.java

@@ -56,7 +56,7 @@ public <T> T construct(final SpecimenType<T> type) {
                 .collect(toList());
 
         if (constructors.isEmpty()) {
-            throw new SpecimenException(format("Cannot construct %s: no public constructor found", type.asClass()));
+            return manufacture(type);
         }
 
         return construct(type, constructors.get(random.nextInt(constructors.size())));
@@ -113,7 +113,7 @@ private <T> T construct(final SpecimenType<T> type, final Constructor<?> constru
                     .map(s -> s.create(new Annotation[0]))
                     .toArray());
         } catch (Exception e) {
-            throw new SpecimenException(format("Unable to construct class %s with constructor %s: %s", type.asClass(), constructor.toString(), e.getMessage()), e);
+            return manufacture(type);
         }
     }
 

src/test/java/com/github/nylle/javafixture/InstanceFactoryTest.java

@@ -1,6 +1,7 @@
 package com.github.nylle.javafixture;
 
 import com.github.nylle.javafixture.testobjects.TestObjectWithGenericConstructor;
+import com.github.nylle.javafixture.testobjects.factorymethod.ConstructorExceptionAndFactoryMethod;
 import com.github.nylle.javafixture.testobjects.factorymethod.TestObjectWithNonPublicFactoryMethods;
 import com.github.nylle.javafixture.testobjects.TestObjectWithPrivateConstructor;
 import com.github.nylle.javafixture.testobjects.factorymethod.FactoryMethodWithArgument;
@@ -67,7 +68,7 @@ void canOnlyUsePublicConstructor() {
 
         assertThatExceptionOfType(SpecimenException.class)
                 .isThrownBy(() -> sut.construct(fromClass(TestObjectWithPrivateConstructor.class)))
-                .withMessageContaining("no public constructor found")
+                .withMessageContaining("Cannot manufacture class")
                 .withNoCause();
     }
 
@@ -80,6 +81,24 @@ void canCreateInstanceFromAbstractClassUsingFactoryMethod() {
         assertThat(actual).isInstanceOf(Charset.class);
     }
 
+    @Test
+    void useFactoryMethodWhenNoConstructorExists() {
+        var sut = new InstanceFactory(new SpecimenFactory(new Context(Configuration.configure())));
+
+        FactoryMethodWithoutArgument result = sut.construct(fromClass(FactoryMethodWithoutArgument.class));
+
+        assertThat(result.getValue()).isEqualTo(42);
+    }
+
+    @Test
+    void fallbackToFactoryMethodWhenConstructorThrowsException() {
+        var sut = new InstanceFactory(new SpecimenFactory(new Context(Configuration.configure())));
+
+        ConstructorExceptionAndFactoryMethod result = sut.construct(new SpecimenType<ConstructorExceptionAndFactoryMethod>() {});
+
+        assertThat(result.getValue()).isNotNull();
+    }
+
     @Nested
     @DisplayName("when manufacturing using factory methods")
     class FactoryMethods {

src/test/java/com/github/nylle/javafixture/testobjects/factorymethod/ConstructorExceptionAndFactoryMethod.java

@@ -0,0 +1,20 @@
+package com.github.nylle.javafixture.testobjects.factorymethod;
+
+public class ConstructorExceptionAndFactoryMethod {
+    private int value;
+
+    public ConstructorExceptionAndFactoryMethod() {
+        throw new IllegalArgumentException("expected for tests");
+    }
+    private ConstructorExceptionAndFactoryMethod(int value) {
+        this.value = value;
+    }
+
+    public static ConstructorExceptionAndFactoryMethod factoryMethod() {
+        return new ConstructorExceptionAndFactoryMethod(42);
+    }
+
+    public int getValue() {
+        return value;
+    }
+}