diff --git a/build.sbt b/build.sbt
index 805cddc..32a8ec6 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,4 +1,4 @@
-val scala3: String = "3.4.2"
+val scala3: String = "3.5.0"
 
 ThisBuild / scalaVersion  := scala3
 ThisBuild / versionScheme := Some("semver-spec")
@@ -9,6 +9,10 @@ ThisBuild / externalResolvers := Seq(
   "Garrity Software Releases" at "https://maven.garrity.co/gs"
 )
 
+ThisBuild / licenses := Seq(
+  "MIT" -> url("https://garrity.co/MIT.html")
+)
+
 val noPublishSettings = Seq(
   publish := {}
 )
diff --git a/modules/core/src/main/scala/gs/test/v0/GsTestError.scala b/modules/core/src/main/scala/gs/test/v0/GsTestError.scala
deleted file mode 100644
index d30e048..0000000
--- a/modules/core/src/main/scala/gs/test/v0/GsTestError.scala
+++ /dev/null
@@ -1,15 +0,0 @@
-package gs.test.v0
-
-sealed trait GsTestError
-
-object GsTestError:
-
-  sealed trait TestDefinitionError extends GsTestError
-
-  object TestDefinitionError:
-
-    case class InvalidIterations(candidate: Int) extends TestDefinitionError
-
-  end TestDefinitionError
-
-end GsTestError
diff --git a/modules/core/src/main/scala/gs/test/v0/Marker.scala b/modules/core/src/main/scala/gs/test/v0/Marker.scala
new file mode 100644
index 0000000..a28ad67
--- /dev/null
+++ b/modules/core/src/main/scala/gs/test/v0/Marker.scala
@@ -0,0 +1,22 @@
+package gs.test.v0
+
+/**
+ * Enumeration for _Markers_, special tokens which "mark" a test to change
+ * execution functionality.
+ *
+ * The basic case for this enumeration is allowing tests to be ignored.
+ *
+ * @param name The formal serialized name of the marker.
+ */
+sealed abstract class Marker(val name: String)
+
+object Marker:
+
+  given CanEqual[Marker, Marker] = CanEqual.derived
+
+  /**
+   * If this [[Marker]] is present on a test, the test will be ignored.
+   */
+  case object Ignored extends Marker("ignored")
+
+end Marker
diff --git a/modules/core/src/main/scala/gs/test/v0/Tag.scala b/modules/core/src/main/scala/gs/test/v0/Tag.scala
new file mode 100644
index 0000000..8e18c5e
--- /dev/null
+++ b/modules/core/src/main/scala/gs/test/v0/Tag.scala
@@ -0,0 +1,24 @@
+package gs.test.v0
+
+import cats.Show
+
+/**
+ * Opaque type representing tags that may be assigned to a [[Test]].
+ */
+opaque type Tag = String
+
+object Tag:
+
+  /**
+   * Instantiate a new [[Tag]].
+   *
+   * @param tag The candidate string.
+   * @return The new [[Tag]] instance.
+   */
+  def apply(tag: String): Tag = tag
+
+  given CanEqual[Tag, Tag] = CanEqual.derived
+
+  given Show[Tag] = tag => tag
+
+end Tag
diff --git a/modules/core/src/main/scala/gs/test/v0/TestDefinition.scala b/modules/core/src/main/scala/gs/test/v0/TestDefinition.scala
index 3a1b4fc..9c2c54c 100644
--- a/modules/core/src/main/scala/gs/test/v0/TestDefinition.scala
+++ b/modules/core/src/main/scala/gs/test/v0/TestDefinition.scala
@@ -2,24 +2,25 @@ package gs.test.v0
 
 import cats.data.EitherT
 import cats.Show
-import gs.test.v0.GsTestError.TestDefinitionError.InvalidIterations
 
 /**
   * Each instance of this class indicates the _definition_ of some test.
   *
   * @param name The display name of the test. Not considered to be unique.
   * @param permanentId The [[PermanentId]] for this test.
-  * @param tags The set of [[Test.Tag]] applicable to this test.
+  * @param documentation The documentation for this test.
+  * @param tags The list of [[Tag]] applicable to this test.
+  * @param markers The list of [[Marker]] applicable to this test.
   * @param iterations The number of iterations of this test to run.
-  * @param f The effect that the test evaluates.
+  * @param unitOfWork The function that the test evaluates.
   */
 final class TestDefinition[F[_]](
   val name: TestDefinition.Name,
   val permanentId: PermanentId,
   val documentation: Option[String],
-  val tags: List[TestDefinition.Tag],
-  val markers: List[TestDefinition.Marker],
-  val iterations: TestDefinition.Iterations,
+  val tags: List[Tag],
+  val markers: List[Marker],
+  val iterations: TestIterations,
   val unitOfWork: EitherT[F, TestFailure, Unit]
 )
 
@@ -47,78 +48,4 @@ object TestDefinition:
 
   end Name
 
-  /**
-   * Opaque type representing tags that may be assigned to a [[Test]].
-   */
-  opaque type Tag = String
-
-  object Tag:
-
-    /**
-     * Instantiate a new [[Test.Tag]].
-     *
-     * @param tag The candidate string.
-     * @return The new [[Test.Tag]] instance.
-     */
-    def apply(tag: String): Tag = tag
-
-    given CanEqual[Tag, Tag] = CanEqual.derived
-
-    given Show[Tag] = tag => tag
-
-  end Tag
-
-  /**
-   * Enumeration for _Markers_, special tokens which "mark" a test to change
-   * execution functionality.
-   *
-   * The basic case for this enumeration is allowing tests to be ignored.
-   *
-   * @param name The formal serialized name of the marker.
-   */
-  sealed abstract class Marker(val name: String)
-
-  object Marker:
-
-    given CanEqual[Marker, Marker] = CanEqual.derived
-
-    /**
-     * If this [[Test.Marker]] is present on a test, the test will be ignored.
-     */
-    case object Ignored extends Marker("ignored")
-
-  end Marker
-
-  /**
-   * Opaque type that represents the number of iterations a test should run.
-   * This value must be at least `1` (the default). To ignore a test, use the
-   * [[Test.Marker.Ignored]] marker.
-   */
-  opaque type Iterations = Int
-
-  object Iterations:
-
-    def One: Iterations = 1
-
-    /**
-     * Validate and instantiate a new [[Iterations]] instance.
-     *
-     * @param candidate The candidate value. Must be 1 or greater.
-     * @return The new [[Iterations]], or an error if an invalid input is given.
-     */
-    def validate(candidate: Int): Either[GsTestError, Iterations] =
-      if candidate < 1 then 
-        Left(InvalidIterations(candidate)) 
-      else 
-        Right(candidate)
-
-    given CanEqual[Iterations, Iterations] = CanEqual.derived
-
-    given Show[Iterations] = iters => iters.toString()
-
-    extension (iters: Iterations)
-      def toInt(): Int = iters
-
-  end Iterations
-
 end TestDefinition
diff --git a/modules/core/src/main/scala/gs/test/v0/TestGroup.scala b/modules/core/src/main/scala/gs/test/v0/TestGroup.scala
index bdbd6d0..a8f53cc 100644
--- a/modules/core/src/main/scala/gs/test/v0/TestGroup.scala
+++ b/modules/core/src/main/scala/gs/test/v0/TestGroup.scala
@@ -3,9 +3,6 @@ package gs.test.v0
 import cats.syntax.all.*
 import cats.effect.Async
 import scala.collection.mutable.ListBuffer
-import gs.test.v0.TestDefinition.Tag
-import gs.test.v0.TestDefinition.Marker
-import gs.test.v0.TestDefinition.Iterations
 import cats.data.EitherT
 import java.util.concurrent.ConcurrentHashMap
 import scala.jdk.CollectionConverters.*
@@ -117,7 +114,7 @@ object TestGroup:
     private val tags: ListBuffer[Tag],
     private val markers: ListBuffer[Marker],
     private var documentation: Option[String] = None,
-    private var iterations: TestDefinition.Iterations = Iterations.One,
+    private var iterations: TestIterations = TestIterations.One,
   ):
     /**
      * Supply documentation for this test.
@@ -164,7 +161,7 @@ object TestGroup:
      * @param iters The number of iterations.
      * @return This builder.
      */
-    def iterate(iters: Iterations): TestBuilder[F] =
+    def iterate(iters: TestIterations): TestBuilder[F] =
       iterations = iters
       this
 
@@ -239,7 +236,7 @@ object TestGroup:
     private val tags: ListBuffer[Tag],
     private val markers: ListBuffer[Marker],
     private var documentation: Option[String] = None,
-    private var iterations: TestDefinition.Iterations = Iterations.One,
+    private var iterations: TestIterations = TestIterations.One,
   ):
     /**
      * Supply documentation for this test.
@@ -286,7 +283,7 @@ object TestGroup:
      * @param iters The number of iterations.
      * @return This builder.
      */
-    def iterate(iters: Iterations): InputTestBuilder[F, Input] =
+    def iterate(iters: TestIterations): InputTestBuilder[F, Input] =
       iterations = iters
       this
 
diff --git a/modules/core/src/main/scala/gs/test/v0/TestGroupDefinition.scala b/modules/core/src/main/scala/gs/test/v0/TestGroupDefinition.scala
index 45bb3f1..7ee6cf6 100644
--- a/modules/core/src/main/scala/gs/test/v0/TestGroupDefinition.scala
+++ b/modules/core/src/main/scala/gs/test/v0/TestGroupDefinition.scala
@@ -9,14 +9,15 @@ import cats.Show
   *
   * @param name The group name. Not considered to be unique.
   * @param documentation Arbitrary documentation for this group of tests.
-  * @param testTags Set of tags applied to all [[Test]] within the group.
+  * @param testTags Set of tags applied to all [[TestDefinition]] within the group.
+  * @param testMarkers Set of markers applied to all [[TestDefinition]] within the group.
   * @param tests The list of tests in this group.
   */
 final class TestGroupDefinition[F[_]](
   val name: TestGroupDefinition.Name,
   val documentation: Option[String],
-  val testTags: List[TestDefinition.Tag],
-  val testMarkers: List[TestDefinition.Marker],
+  val testTags: List[Tag],
+  val testMarkers: List[Marker],
   val beforeGroup: Option[F[Unit]],
   val afterGroup: Option[F[Unit]],
   val beforeEachTest: Option[F[Unit]],
@@ -27,7 +28,7 @@ final class TestGroupDefinition[F[_]](
 object TestGroupDefinition:
 
   /**
-   * Opaque type representing names that may be assigned to [[TestGroup]].
+   * Opaque type representing names that may be assigned to test groups.
    */
   opaque type Name = String
 
diff --git a/modules/core/src/main/scala/gs/test/v0/TestIterations.scala b/modules/core/src/main/scala/gs/test/v0/TestIterations.scala
new file mode 100644
index 0000000..6bea812
--- /dev/null
+++ b/modules/core/src/main/scala/gs/test/v0/TestIterations.scala
@@ -0,0 +1,37 @@
+package gs.test.v0
+
+import cats.Show
+
+/**
+ * Opaque type that represents the number of iterations a test should run.
+ * This value must be at least `1` (the default). To ignore a test, use the
+ * [[Test.Marker.Ignored]] marker.
+ */
+opaque type TestIterations = Int
+
+object TestIterations:
+
+  def One: TestIterations = 1
+
+  /**
+   * Validate and instantiate a new [[TestIterations]] instance.
+   *
+   * @param candidate The candidate value. Must be 1 or greater.
+   * @return The new [[TestIterations]], or an error if an invalid input is given.
+   */
+  def apply(candidate: Int): TestIterations =
+    if candidate < 1 then 
+      throw new IllegalArgumentException(
+        s"Tests must iterate at least once. Received candidate '$candidate'."
+      )
+    else 
+      candidate
+
+  given CanEqual[TestIterations, TestIterations] = CanEqual.derived
+
+  given Show[TestIterations] = iters => iters.toString()
+
+  extension (iters: TestIterations)
+    def toInt(): Int = iters
+
+end TestIterations
diff --git a/modules/core/src/main/scala/gs/test/v0/syntax.scala b/modules/core/src/main/scala/gs/test/v0/syntax.scala
new file mode 100644
index 0000000..742a5ab
--- /dev/null
+++ b/modules/core/src/main/scala/gs/test/v0/syntax.scala
@@ -0,0 +1,25 @@
+package gs.test.v0
+
+/**
+  * String interpolator for [[Tag]]. Shorthand for producing new [[Tag]] 
+  * instances.
+  *
+  * {{{
+  * import gs.test.v0.*
+  * val tag1: TestDefinition.Tag = tag"example"
+  * }}}
+  */
+extension (sc: StringContext)
+  def tag(args: Any*): Tag = Tag(sc.s(args*))
+
+/**
+  * String interpolator for [[PermanentId]]. Shorthand for producing new 
+  * [[PermanentId]] instances.
+  *
+  * {{{
+  * import gs.test.v0.*
+  * val permanentId: PermanentId = pid"example"
+  * }}}
+  */
+extension (sc: StringContext)
+  def pid(args: Any*): PermanentId = PermanentId(sc.s(args*))
diff --git a/modules/core/src/test/scala/gs/test/v0/GroupImplementationTests.scala b/modules/core/src/test/scala/gs/test/v0/GroupImplementationTests.scala
index a6109d8..8d0b754 100644
--- a/modules/core/src/test/scala/gs/test/v0/GroupImplementationTests.scala
+++ b/modules/core/src/test/scala/gs/test/v0/GroupImplementationTests.scala
@@ -1,6 +1,9 @@
 package gs.test.v0
 
 import munit.*
+import cats.effect.IO
+
+import gs.test.v0.{Tag => GsTag}
 
 class GroupImplementationTests extends FunSuite:
   import GroupImplementationTests.* 
@@ -25,7 +28,55 @@ class GroupImplementationTests extends FunSuite:
         assertEquals(t.documentation, None)
         assertEquals(t.tags, List.empty)
         assertEquals(t.markers, List.empty)
-        assertEquals(t.iterations, TestDefinition.Iterations.One)
+        assertEquals(t.iterations, TestIterations.One)
+      case _ => fail("Unexpected number of defined tests.")
+  }
+
+  test("should support a group with all values set") {
+    val g2 = new G2
+    val group = g2.toGroupDefinition()
+    assertEquals(group.name, TestGroupDefinition.Name("G2"))
+    assertEquals(group.documentation, Some("docs"))
+    assertEquals(group.testTags, List(GsTag("tag")))
+    assertEquals(group.testMarkers, List(Marker.Ignored))
+    assertEquals(group.beforeGroup.isDefined, true)
+    assertEquals(group.afterGroup.isDefined, true)
+    assertEquals(group.beforeEachTest.isDefined, true)
+    assertEquals(group.afterEachTest.isDefined, true)
+    assertEquals(group.tests.size, 1)
+
+    group.tests match
+      case t :: Nil =>
+        assertEquals(t.name, TestDefinition.Name("inherit from group"))
+        assertEquals(t.permanentId, Ids.T2)
+        assertEquals(t.documentation, None)
+        assertEquals(t.tags, List(GsTag("tag")))
+        assertEquals(t.markers, List(Marker.Ignored))
+        assertEquals(t.iterations, TestIterations.One)
+      case _ => fail("Unexpected number of defined tests.")
+  }
+
+  test("should support a simple group with a configured test") {
+    val g3 = new G3
+    val group = g3.toGroupDefinition()
+    assertEquals(group.name, TestGroupDefinition.Name("G3"))
+    assertEquals(group.documentation, None)
+    assertEquals(group.testTags, List.empty)
+    assertEquals(group.testMarkers, List.empty)
+    assertEquals(group.beforeGroup, None)
+    assertEquals(group.afterGroup, None)
+    assertEquals(group.beforeEachTest, None)
+    assertEquals(group.afterEachTest, None)
+    assertEquals(group.tests.size, 1)
+
+    group.tests match
+      case t :: Nil =>
+        assertEquals(t.name, TestDefinition.Name("configure test"))
+        assertEquals(t.permanentId, Ids.T3)
+        assertEquals(t.documentation, Some("docs"))
+        assertEquals(t.tags, List(tag"tag1", tag"tag2"))
+        assertEquals(t.markers, List(Marker.Ignored))
+        assertEquals(t.iterations, TestIterations(2))
       case _ => fail("Unexpected number of defined tests.")
   }
 
@@ -33,7 +84,9 @@ object GroupImplementationTests:
 
   object Ids:
 
-    val T1: PermanentId = PermanentId("t1")
+    val T1: PermanentId = pid"t1"
+    val T2: PermanentId = pid"t2"
+    val T3: PermanentId = pid"t3"
 
   end Ids
 
@@ -42,4 +95,36 @@ object GroupImplementationTests:
     test(Ids.T1, "simple").pure { Right(()) }
   end G1
 
+  class G2 extends TestGroup.IO:
+    override def name: String = 
+      "G2"
+
+    override def documentation: Option[String] = 
+      Some("docs")
+
+    override def tags: List[GsTag] = 
+      List(GsTag("tag"))
+
+    override def markers: List[Marker] = 
+      List(Marker.Ignored)
+
+    beforeGroup { IO.unit }
+    afterGroup { IO.unit }
+    beforeEachTest { IO.unit }
+    afterEachTest { IO.unit }
+
+    test(Ids.T2, "inherit from group").pure { Right(()) }
+  end G2
+
+  class G3 extends TestGroup.IO:
+    override def name: String = "G3"
+
+    test(Ids.T3, "configure test")
+      .document("docs")
+      .tagged(tag"tag1", tag"tag2")
+      .marked(Marker.Ignored)
+      .iterate(TestIterations(2))
+      .pure { Right(()) }
+  end G3
+
 end GroupImplementationTests
diff --git a/project/plugins.sbt b/project/plugins.sbt
index c708d3a..eb382dc 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -29,5 +29,5 @@ externalResolvers := Seq(
 )
 
 addSbtPlugin("org.scoverage" % "sbt-scoverage"        % "2.1.0")
-addSbtPlugin("gs"            % "sbt-garrity-software" % "0.3.0")
+addSbtPlugin("gs"            % "sbt-garrity-software" % "0.4.0")
 addSbtPlugin("gs"            % "sbt-gs-semver"        % "0.3.0")