diff --git a/modules/core/src/main/scala/gs/graph/v0/Adjacency.scala b/modules/core/src/main/scala/gs/graph/v0/Adjacency.scala
index 214b8b1..67a825c 100644
--- a/modules/core/src/main/scala/gs/graph/v0/Adjacency.scala
+++ b/modules/core/src/main/scala/gs/graph/v0/Adjacency.scala
@@ -79,7 +79,7 @@ sealed trait Adjacency:
     val notContained = vertices.filterNot(contains)
     if notContained.nonEmpty then
       throw GraphException.AdjacencyDoesNotContainVertices(
-        vertices,
+        notContained,
         numberOfVertices
       )
     else
@@ -109,16 +109,6 @@ object Adjacency:
 
   given CanEqual[Adjacency, Adjacency] = CanEqual.derived
 
-  /** Instantiate a new [[Adjacency]] list from a raw representation.
-    *
-    * @param adj
-    *   The underlying vector of values.
-    * @return
-    *   The new [[Adjacency]].
-    */
-  def apply(adj: Vector[Vector[Vertex]]): Adjacency =
-    DefaultAdjacency.apply(adj)
-
   /** Create an empty adjacency list for some number of vertices. No vertex has
     * any connections to another vertex.
     *
@@ -269,19 +259,6 @@ final class DefaultAdjacency private (
 
 object DefaultAdjacency:
 
-  /** Instantiate a new [[Adjacency]] list from a raw representation.
-    *
-    * @param adj
-    *   The underlying vector of values.
-    * @return
-    *   The new [[Adjacency]].
-    */
-  def apply(adj: Vector[Vector[Vertex]]): Adjacency =
-    new DefaultAdjacency(
-      numberOfVertices = Size.fromVector(adj),
-      neighbors = adj
-    )
-
   /** Create an empty adjacency list for some number of vertices. No vertex has
     * any connections to another vertex.
     *
@@ -462,7 +439,10 @@ object MappedAdjacency:
   ): Adjacency =
     val acc = scala.collection.mutable.Map.empty[Vertex, ListBuffer[Vertex]]
     edges.foreach { edge =>
-      acc.getOrElseUpdate(edge.from, ListBuffer.empty).addOne(edge.to)
+      val _ = acc.getOrElseUpdate(edge.from, ListBuffer.empty).addOne(edge.to)
+      // Accounts for vertices with no outgoing edges.
+      // They should still be present as vertices in the graph.
+      val _ = acc.getOrElseUpdate(edge.to, ListBuffer.empty)
     }
     val neighbors = acc.map { case (v, ns) => v -> ns.toVector }.toMap
     new MappedAdjacency(Size.of(neighbors), neighbors)
diff --git a/modules/core/src/main/scala/gs/graph/v0/GraphException.scala b/modules/core/src/main/scala/gs/graph/v0/GraphException.scala
index ff4a8fb..d094be9 100644
--- a/modules/core/src/main/scala/gs/graph/v0/GraphException.scala
+++ b/modules/core/src/main/scala/gs/graph/v0/GraphException.scala
@@ -1,9 +1,19 @@
 package gs.graph.v0
 
+/** Root for all exceptions in the `gs-graph` library.
+  */
 sealed abstract class GraphException extends Throwable
 
 object GraphException:
 
+  /** Thrown when attempting to leverage a vertex with a bounded adjacency, and
+    * the vertex exceeds the bounds of that graph (adjacency).
+    *
+    * @param vertex
+    *   The vertex in question.
+    * @param bound
+    *   The bound (maximum vertex value) of the graph.
+    */
   case class VertexExceedsGraphBounds(
     vertex: Vertex,
     bound: Size
@@ -12,6 +22,14 @@ object GraphException:
     override def getMessage(): String =
       s"Vertex '$vertex' exceeds graph bound of '$bound' vertices."
 
+  /** Thrown when instantiating a data graph, but the wrong amount of data is
+    * provided.
+    *
+    * @param numberOfVertices
+    *   The number of vertices in the graph.
+    * @param quantityOfData
+    *   The number of data entries provided.
+    */
   case class DataGraphMismatch(
     numberOfVertices: Size,
     quantityOfData: Int
@@ -21,16 +39,14 @@ object GraphException:
       s"""Attempted to initialize a data graph with '$numberOfVertices'
           vertices. '$quantityOfData' data values were provided.""".stripMargin
 
-  case class RootOutOfBounds(
-    root: Vertex,
-    numberOfVertices: Size
-  ) extends GraphException:
-
-    override def getMessage(): String =
-      s"""Attempted to instantiate a single-root digraph with root '$root',
-          but that root exceeds the graph bound of '$numberOfVertices'
-          vertices.""".stripMargin
-
+  /** Thrown when some collection of vertices are expected within an adjacency,
+    * but not found.
+    *
+    * @param vertices
+    *   The collection of expected vertices.
+    * @param numberOfVertices
+    *   The size of the underlying adjacency.
+    */
   case class AdjacencyDoesNotContainVertices(
     vertices: Iterable[Vertex],
     numberOfVertices: Size
@@ -40,6 +56,14 @@ object GraphException:
       s"""The following vertices were not found within an Adjacency of size
           '$numberOfVertices': [${vertices.mkString(", ")}]""".stripMargin
 
+  /** Thrown when some candidate neighbor is defined, but not contained within
+    * the adjacency as a vertex. This indicates a malformed structure.
+    *
+    * @param candidate
+    *   The candidate neighbor vertex.
+    * @param vertex
+    *   The vertex that uses the neighbor.
+    */
   case class NeighborNotContainedByAdjacency(
     candidate: Vertex,
     vertex: Vertex
diff --git a/modules/core/src/test/scala/gs/graph/v0/AdjacencyTests.scala b/modules/core/src/test/scala/gs/graph/v0/AdjacencyTests.scala
index afc3dbb..3e6dcaf 100644
--- a/modules/core/src/test/scala/gs/graph/v0/AdjacencyTests.scala
+++ b/modules/core/src/test/scala/gs/graph/v0/AdjacencyTests.scala
@@ -19,6 +19,9 @@ class AdjacencyTests extends munit.FunSuite:
     4 -> 6
   )
 
+  private val vertices =
+    edges.flatMap(edge => List(edge.from, edge.to)).distinct
+
   private val adj = Adjacency.fromEdges(size, edges)
 
   test("should provide equality") {
@@ -102,3 +105,75 @@ class AdjacencyTests extends munit.FunSuite:
     assertEquals(a.numberOfVertices, expectedSize)
     assertEquals(a.numberOfEdges, Size.of(es))
   }
+
+  test(
+    "should fail to take a subset of vertices not contained within the source"
+  ) {
+    val subset = Set(V(0), V(1), V(5))
+    val es     = Edge.list(0 -> 1, 1 -> 2, 2 -> 0)
+    val a      = Adjacency.fromEdges(es)
+
+    Try(a.subset(subset)) match
+      case Failure(ex: GraphException.AdjacencyDoesNotContainVertices) =>
+        assertEquals(ex.vertices, Set(V(5)))
+        assertEquals(ex.numberOfVertices, a.numberOfVertices)
+      case _ => fail("Expected the subset operation to fail.")
+  }
+
+  test("should represent a single arbitrary vertex") {
+    val v = V(9)
+    val a = Adjacency.single(v)
+    assertEquals(a.numberOfVertices, Size.One)
+    assertEquals(a.numberOfEdges, Size.Zero)
+    assertEquals(a.contains(v), true)
+    assertEquals(a.contains(V(0)), false)
+  }
+
+  test("should instantiate an adjacency from mapped edges") {
+    val es = Edge.list(7 -> 8, 8 -> 9, 9 -> 5)
+    val vs = es.flatMap(edge => List(edge.v1, edge.v2))
+    val a  = Adjacency.fromEdgesMapped(es)
+    assertEquals(a.numberOfVertices, Size(4))
+    assertEquals(a.numberOfEdges, Size.of(es))
+    es.foreach { edge =>
+      assertEquals(a.contains(edge.v1), true)
+      assertEquals(a.contains(edge.v2), true)
+    }
+    a.vertices.foreach(vertex => assertEquals(vs.contains(vertex), true))
+    assertEquals(a.toEdges(), es.toVector)
+    assertEquals(a.incoming(V(7)), Vector.empty)
+    assertEquals(a.incoming(V(8)), Vector(V(7)))
+    assertEquals(a.incoming(V(9)), Vector(V(8)))
+    assertEquals(a.incoming(V(5)), Vector(V(9)))
+  }
+
+  test(
+    "should return an empty vector when finding a vertex that is not present"
+  ) {
+    val es = Edge.list(0 -> 1, 1 -> 2, 2 -> 3)
+    val a1 = Adjacency.fromEdges(es)
+    val a2 = Adjacency.fromEdgesMapped(es)
+    assertEquals(a1.at(V(9)), Vector.empty)
+    assertEquals(a2.at(V(9)), Vector.empty)
+  }
+
+  test("should instantiate an adjacency from edges (size-based)") {
+    val a = Adjacency.fromEdges(edges)
+    a.vertices.foreach(v => assertEquals(vertices.contains(v), true))
+    assertEquals(a.numberOfVertices, Size.of(vertices))
+    assertEquals(a.numberOfEdges, Size.of(edges))
+  }
+
+  test(
+    "should fail to validate a mapped adjacency when a neighbor is not contained in the keyset"
+  ) {
+    val input = Map(
+      V(0) -> Vector(V(1), V(2)),
+      V(1) -> Vector.empty
+    )
+    Try(MappedAdjacency.validate(input)) match
+      case Failure(ex: GraphException.NeighborNotContainedByAdjacency) =>
+        assertEquals(ex.candidate, V(2))
+        assertEquals(ex.vertex, V(0))
+      case _ => fail("Expected adjacency validation to fail.")
+  }
diff --git a/modules/core/src/test/scala/gs/graph/v0/GraphExceptionTests.scala b/modules/core/src/test/scala/gs/graph/v0/GraphExceptionTests.scala
new file mode 100644
index 0000000..6509faf
--- /dev/null
+++ b/modules/core/src/test/scala/gs/graph/v0/GraphExceptionTests.scala
@@ -0,0 +1,57 @@
+package gs.graph.v0
+
+import gs.graph.v0.syntax.V
+import munit.*
+
+class GraphExceptionTests extends FunSuite:
+
+  test("should VertexExceedsGraphBounds") {
+    val v  = V(2)
+    val b  = Size(1)
+    val ex = GraphException.VertexExceedsGraphBounds(v, b)
+    assertEquals(ex.vertex, v)
+    assertEquals(ex.bound, b)
+    assertEquals(
+      ex.getMessage(),
+      s"Vertex '$v' exceeds graph bound of '$b' vertices."
+    )
+  }
+
+  test("should DataGraphMismatch") {
+    val n  = Size(2)
+    val q  = 1
+    val ex = GraphException.DataGraphMismatch(n, q)
+    assertEquals(ex.numberOfVertices, n)
+    assertEquals(ex.quantityOfData, q)
+    assertEquals(
+      ex.getMessage(),
+      s"""Attempted to initialize a data graph with '$n'
+          vertices. '$q' data values were provided.""".stripMargin
+    )
+  }
+
+  test("should AdjacencyDoesNotContainVertices") {
+    val vs = List(V(8), V(9))
+    val n  = Size(4)
+    val ex = GraphException.AdjacencyDoesNotContainVertices(vs, n)
+    assertEquals(ex.vertices, vs)
+    assertEquals(ex.numberOfVertices, n)
+    assertEquals(
+      ex.getMessage(),
+      s"""The following vertices were not found within an Adjacency of size
+          '$n': [${vs.mkString(", ")}]""".stripMargin
+    )
+  }
+
+  test("should NeighborNotContainedByAdjacency") {
+    val c  = V(9)
+    val v  = V(0)
+    val ex = GraphException.NeighborNotContainedByAdjacency(c, v)
+    assertEquals(ex.candidate, c)
+    assertEquals(ex.vertex, v)
+    assertEquals(
+      ex.getMessage(),
+      s"""Attempted to reference neighbor '$c' of vertex '$v', but
+          '$c' is not a valid vertex in the adjacency.""".stripMargin
+    )
+  }