just build both graphs at the same time.

node.go

@@ -7,10 +7,43 @@ func nextNodeID() int {
 	return lastID
 }
 
-type node struct {
+// lnode is a node in the logical graph. Developers create a logical graph in
+// which nodes may have more than one parent. Each test value written by a
+// developer appears as one logical node in the logical graph. The public
+// documentation refers to the logical graph as simply the test graph.
+type lnode struct {
 	id       int
-	test     Test
 	name     string
-	parents  []*node
-	children []*node
+	xnodes   []*xnode
+	parents  []*lnode
+	children []*lnode
+}
+
+// child adds an lnode as a child of the receiver. For every xnode in this
+// lnode, the child lnode has a component xnode whose parent is the
+// corresponding xnode in this lnode.
+func (l *lnode) child(c *lnode, t Test) {
+	c.parents = append(c.parents, l)
+	l.children = append(l.children, c)
+	for _, x := range l.xnodes {
+		xchild := x.child(t)
+		xchild.lnode = c
+		c.xnodes = append(c.xnodes, xchild)
+	}
+}
+
+// xnode is a node in the execution graph, representing one instance of a test
+// to be executed. xnode is the unit test in tea. every xnode is either
+// unparented or has one parent.
+type xnode struct {
+	lnode    *lnode
+	test     Test
+	parent   *xnode
+	children []*xnode
+}
+
+func (x *xnode) child(t Test) *xnode {
+	child := &xnode{test: t, parent: x}
+	x.children = append(x.children, child)
+	return child
 }

selection.go

@@ -1,41 +1,38 @@
 package tea
 
-import (
-	"testing"
-)
-
 func NewSelection(test Test) Selection {
-	n := node{test: test}
-	return Selection{
-		nodes: []*node{&n},
+	x := xnode{
+		test: clone(test),
 	}
-}
-
-func RunSelection(t *testing.T, s Selection) {
+	l := lnode{
+		id:     nextNodeID(),
+		name:   parseName(test),
+		xnodes: []*xnode{&x},
+	}
+	x.lnode = &l
 
+	return Selection{
+		nodes: []*lnode{&l},
+	}
 }
 
+// Selection represents a set of nodes in our graph.
 type Selection struct {
-	nodes []*node
+	nodes []*lnode
 }
 
 func (s Selection) Child(test Test) Selection {
-	child := &node{
-		id:      nextNodeID(),
-		test:    test,
-		name:    parseName(test),
-		parents: s.nodes,
-	}
-	for _, sn := range s.nodes {
-		sn.children = append(sn.children, child)
+	child := &lnode{id: nextNodeID(), name: parseName(test)}
+	for _, l := range s.nodes {
+		l.child(child, test)
 	}
-	return Selection{nodes: []*node{child}}
+	return Selection{nodes: []*lnode{child}}
 }
 
 func (s Selection) And(other Selection) Selection {
 	included := make(map[int]bool)
 
-	out := make([]*node, 0, len(s.nodes)+len(other.nodes))
+	out := make([]*lnode, 0, len(s.nodes)+len(other.nodes))
 	for _, n := range append(s.nodes, other.nodes...) {
 		if !included[n.id] {
 			out = append(out, n)

selection_test.go

@@ -1 +1,21 @@
 package tea
+
+import (
+	"testing"
+)
+
+func TestNewSelection(t *testing.T) {
+	s := NewSelection(Passing("A"))
+	if len(s.nodes) != 1 {
+		t.Fatalf("expected 1 node in new selection, saw %d", len(s.nodes))
+	}
+
+	l := s.nodes[0]
+	if len(l.children) != 0 {
+		t.Fatalf("new selection should not have any children, but has %d", len(l.children))
+	}
+
+	if len(l.xnodes) != 1 {
+		t.Fatalf("expected 1 xnode in lnode, saw %d", len(l.xnodes))
+	}
+}

test.go

@@ -18,9 +18,13 @@ type Test interface {
 // like, kinda on you though, I can't really enforce things that the Go type
 // system doesn't let me enforce.
 func clone(t Test) Test {
-	srcV := reflect.ValueOf(t).Elem()
-	destV := reflect.New(srcV.Type())
-	destV.Elem().Set(srcV)
+	v := reflect.ValueOf(t)
+	switch v.Kind() {
+	case reflect.Ptr:
+		v = v.Elem()
+	}
+	destV := reflect.New(v.Type())
+	destV.Elem().Set(v)
 	return destV.Interface().(Test)
 }