First cut - demonstrates the hooks mechanism.

src/main/java/com/greghaskins/spectrum/AbstractSupplyingHook.java

@@ -0,0 +1,47 @@
+package com.greghaskins.spectrum;
+
+import static com.greghaskins.spectrum.Spectrum.assertSpectrumInTestMode;
+
+import com.greghaskins.spectrum.model.Singleton;
+
+/**
+ * A base class for supplying hooks to use. Override before or after. Return the singleton
+ * value from the before method.
+ * You can use this to write any plugin which needs to make a value visible to the specs.
+ * This is not the only way to achieve that - you can also build from {@link SupplyingHook}
+ * but this captures the template for a complex hook.
+ */
+public class AbstractSupplyingHook<T> extends Singleton<T> implements SupplyingHook<T> {
+  /**
+   * Override this to supply behaviour for before the block is run.
+   * @return the value that the singleton will store to supply
+   */
+  protected T before() {
+    return null;
+  }
+
+  /**
+   * Override this to supply behaviour for after the block is run.
+   */
+  protected void after() {}
+
+  /**
+   * Template method for a hook which supplies.
+   * @param block the inner block that will be run
+   * @throws Throwable on error
+   */
+  @Override
+  public void acceptOrThrow(Block block) throws Throwable {
+    set(before());
+    block.run();
+    after();
+    clear();
+  }
+
+  @Override
+  public T get() {
+    assertSpectrumInTestMode();
+
+    return super.get();
+  }
+}

src/main/java/com/greghaskins/spectrum/CompositeTest.java

@@ -0,0 +1,41 @@
+package com.greghaskins.spectrum;
+
+import com.greghaskins.spectrum.internal.Atomic;
+import com.greghaskins.spectrum.internal.Child;
+import com.greghaskins.spectrum.internal.FailureDetectingRunListener;
+import com.greghaskins.spectrum.internal.Parent;
+import com.greghaskins.spectrum.model.TaggingState;
+
+import org.junit.runner.Description;
+import org.junit.runner.notification.RunNotifier;
+
+/**
+ * Subclass of {@link Suite} that represent the fact that some tests are composed
+ * of interrelated steps which add up to a single test.
+ */
+final class CompositeTest extends Suite implements Atomic {
+  /**
+   * Constructs a Composite Test, which is a suite run as an atomic test.
+   * @param description of the test
+   * @param parent parent suite
+   * @param tagging tagging state to inherit from parent
+   */
+  CompositeTest(final Description description, final Parent parent, final TaggingState tagging) {
+    super(description, parent, CompositeTest::abortOnFailureChildRunner, tagging);
+  }
+
+  private static void abortOnFailureChildRunner(final Suite suite, final RunNotifier runNotifier) {
+    FailureDetectingRunListener listener = new FailureDetectingRunListener();
+    runNotifier.addListener(listener);
+    try {
+      for (Child child : suite.children) {
+        if (listener.hasFailedYet()) {
+          child.ignore();
+        }
+        suite.runChild(child, runNotifier);
+      }
+    } finally {
+      runNotifier.removeListener(listener);
+    }
+  }
+}

src/main/java/com/greghaskins/spectrum/Configuration.java

@@ -1,5 +1,9 @@
 package com.greghaskins.spectrum;
 
+/**
+ * Allows the injection of suite configuration during test definition. A wrapper for the
+ * suite which exposes configurables.
+ */
 public class Configuration {
 
   private final Suite suite;

src/main/java/com/greghaskins/spectrum/Hook.java

@@ -0,0 +1,11 @@
+package com.greghaskins.spectrum;
+
+/**
+ * A hook allows you to inject functionality before and/or after a {@link Block}.
+ * Just implement the {@link ThrowingConsumer#acceptOrThrow(Object)} method and
+ * call {@link Block#run()} within your implementation.
+ * If your hook is going to provide an object to the running test, then implement
+ * {@link SupplyingHook} or subclass {@link AbstractSupplyingHook}.
+ */
+public interface Hook extends ThrowingConsumer<Block> {
+}

src/main/java/com/greghaskins/spectrum/Spec.java

@@ -1,9 +1,14 @@
 package com.greghaskins.spectrum;
 
+import com.greghaskins.spectrum.internal.Atomic;
+import com.greghaskins.spectrum.internal.Child;
+import com.greghaskins.spectrum.internal.NotifyingBlock;
+import com.greghaskins.spectrum.internal.Parent;
+
 import org.junit.runner.Description;
 import org.junit.runner.notification.RunNotifier;
 
-final class Spec implements Child {
+final class Spec implements Child, Atomic {
 
   private final NotifyingBlock block;
   private final Description description;

src/main/java/com/greghaskins/spectrum/Spectrum.java

@@ -1,8 +1,12 @@
 package com.greghaskins.spectrum;
 
-import static com.greghaskins.spectrum.PreConditionBlock.with;
-import static com.greghaskins.spectrum.PreConditions.Factory.focus;
-import static com.greghaskins.spectrum.PreConditions.Factory.ignore;
+import static com.greghaskins.spectrum.internal.PreConditionBlock.with;
+import static com.greghaskins.spectrum.model.PreConditions.Factory.focus;
+import static com.greghaskins.spectrum.model.PreConditions.Factory.ignore;
+
+import com.greghaskins.spectrum.internal.LetHook;
+import com.greghaskins.spectrum.model.ConstructorBlock;
+import com.greghaskins.spectrum.model.HookContext;
 
 import org.junit.AssumptionViolatedException;
 import org.junit.runner.Description;
@@ -249,17 +253,24 @@ public static void afterAll(final com.greghaskins.spectrum.Block block) {
    *        `Throwable`
    * @return memoized supplier
    */
-  public static <T> Supplier<T> let(final ThrowingSupplier<T> supplier) {
-    final ConcurrentHashMap<Supplier<T>, T> cache = new ConcurrentHashMap<>(1);
-    afterEach(cache::clear);
-
-    return () -> {
-      if (getCurrentSuiteBeingDeclared() == null) {
-        return cache.computeIfAbsent(supplier, Supplier::get);
-      }
-      throw new IllegalStateException("Cannot use the value from let() in a suite declaration. "
+  public static <T> Supplier<T> let(final com.greghaskins.spectrum.ThrowingSupplier<T> supplier) {
+    LetHook<T> letHook = new LetHook<>(supplier);
+    HookContext hookContext = new HookContext(letHook, false, false, true);
+    getCurrentSuiteBeingDeclared().addHook(hookContext);
+
+    return letHook;
+  }
+
+  /**
+   * Will throw an exception if this method happens to be called while Spectrum is still defining
+   * tests, rather than executing them. Useful to see if a hook is being accidentally used
+   * during definition.
+   */
+  public static void assertSpectrumInTestMode() {
+    if (getCurrentSuiteBeingDeclared() != null) {
+      throw new IllegalStateException("Cannot use this statement in a suite declaration. "
           + "It may only be used in the context of a running spec.");
-    };
+    }
   }
 
   /**
@@ -271,27 +282,9 @@ public static <T> Supplier<T> let(final ThrowingSupplier<T> supplier) {
    *
    * @param <T> The type of result that will be supplied
    */
+  @Deprecated
   @FunctionalInterface
-  public interface ThrowingSupplier<T> extends Supplier<T> {
-
-    /**
-     * Get a result.
-     *
-     * @return a result
-     * @throws Throwable any uncaught Error or Exception
-     */
-    T getOrThrow() throws Throwable;
-
-    @Override
-    default T get() {
-      try {
-        return getOrThrow();
-      } catch (final RuntimeException | Error unchecked) {
-        throw unchecked;
-      } catch (final Throwable checked) {
-        throw new RuntimeException(checked);
-      }
-    }
+  public interface ThrowingSupplier<T> extends com.greghaskins.spectrum.ThrowingSupplier<T> {
   }