Actually try to inject values when determining if we can resolve a pa…

…rameter.

Fix #2

disable-extension/pom.xml

@@ -1,5 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
 
   <parent>

guice-extension/src/main/java/name/falgout/jeffrey/testing/junit/guice/GuiceExtension.java

@@ -7,10 +7,12 @@
 import com.google.common.reflect.TypeToken;
 import com.google.inject.AbstractModule;
 import com.google.inject.BindingAnnotation;
+import com.google.inject.ConfigurationException;
 import com.google.inject.Guice;
 import com.google.inject.Injector;
 import com.google.inject.Key;
 import com.google.inject.Module;
+import com.google.inject.ProvisionException;
 import java.lang.annotation.Annotation;
 import java.lang.reflect.AnnotatedElement;
 import java.lang.reflect.Constructor;
@@ -199,7 +201,16 @@ public boolean supportsParameter(ParameterContext parameterContext,
         extensionContext.getTestClass(),
         parameter);
     Optional<Injector> optInjector = getInjectorForParameterResolution(extensionContext);
-    return optInjector.map(injector -> injector.getExistingBinding(key)).isPresent();
+    return optInjector.filter(injector -> {
+      try {
+        injector.getInstance(key);
+        return true;
+      } catch (ConfigurationException | ProvisionException e) {
+        // If we throw a ParameterResolutionException here instead of returning false, we'll block
+        // other ParameterResolvers from being able to work.
+        return false;
+      }
+    }).isPresent();
   }
 
   @Override
@@ -250,7 +261,8 @@ private static Key<?> getKey(Optional<Class<?>> containingElement, Parameter par
   }
 
   /**
-   * @throws IllegalArgumentException if the given element has more than one binding annotation.
+   * @throws IllegalArgumentException if the given element has more than one binding
+   *     annotation.
    */
   private static Optional<? extends Annotation> getOnlyBindingAnnotation(AnnotatedElement element) {
     return Optional.ofNullable(Iterables.getOnlyElement(getBindingAnnotations(element), null));

guice-extension/src/test/java/name/falgout/jeffrey/testing/junit/guice/GuiceExtensionTest.java

@@ -83,6 +83,14 @@ void canInjectQualifiedParameters(@SomeBindingAnnotation String bound) {
     assertThat(bound).isEqualTo(TestModule.BOUND);
   }
 
+  @Test
+  void canInjectJustInTimeBindings(
+      @SomeBindingAnnotation String bound,
+      ImplicitlyInjectable justInTime) {
+    assertThat(justInTime).isNotNull();
+    assertThat(justInTime.getArg()).isEqualTo(bound);
+  }
+
   @SuppressWarnings("unused")
   @IncludeModule(TestModule.class)
   static abstract class BaseType {
@@ -151,7 +159,13 @@ void moduleConstructorThrowsException(String string) {}
         @Cause(type = ParameterResolutionException.class, message = "No ParameterResolver")
     )
     @Test
-    void doNotHaveBinding(NegativeExamples examples) {}
+    void doesNotHaveInjectConstructor(NotInjectable.Arg arg) {}
+
+    @ExpectFailure(
+        @Cause(type = ParameterResolutionException.class, message = "No ParameterResolver")
+    )
+    @Test
+    void cannotBeInjected(NotInjectable notInjectable) {}
   }
 
   static final class FooBarExtension implements ParameterResolver {
@@ -214,4 +228,26 @@ public BadModule2() {
     @Override
     protected void configure() {}
   }
+
+  private static class ImplicitlyInjectable {
+    private String arg;
+
+    @Inject
+    ImplicitlyInjectable(@SomeBindingAnnotation String arg) {
+      this.arg = arg;
+    }
+
+    public String getArg() {
+      return arg;
+    }
+  }
+
+  private static class NotInjectable {
+    @Inject
+    NotInjectable(Arg arg) {}
+
+    private static class Arg {
+      private Arg(String s) {}
+    }
+  }
 }