export a Passing type

I keep writing these one-off when I actually use tea. It seems like it's
worth including. It's especially useful for the root test, where you
don't necessarily want to create a test, but want to create a starting
environment. Exporting a type that always passes is preferrable to
making an explicit environment type, since we can maintain our
guarantees that our environment isn't an invalid value.

env.go

@@ -25,6 +25,10 @@ func (e *env) save(test Test) *env {
 	}
 	T := V.Type()
 
+	if T.Kind() != reflect.Struct {
+		return e
+	}
+
 	saved := make(map[string]interface{})
 	for i := 0; i < T.NumField(); i++ {
 		f := T.Field(i)

env_test.go

@@ -6,7 +6,7 @@ import (
 
 func TestSave(t *testing.T) {
 	t.Run("empty begets nil", func(t *testing.T) {
-		e := mkenv(new(empty))
+		e := mkenv(Pass)
 		if e != nil {
 			t.Errorf("saw unexpected env value looking for nil: %v", e)
 		}
@@ -14,7 +14,7 @@ func TestSave(t *testing.T) {
 
 	t.Run("unexported fields are ignored", func(t *testing.T) {
 		type test struct {
-			empty
+			Passing
 			foo int `tea:"save"`
 		}
 
@@ -25,7 +25,7 @@ func TestSave(t *testing.T) {
 
 	t.Run("create an env from a test", func(t *testing.T) {
 		test := struct {
-			empty
+			Passing
 			Foo int `tea:"save"`
 		}{
 			Foo: 5,
@@ -48,7 +48,7 @@ func TestSave(t *testing.T) {
 
 	t.Run("update an existing env", func(t *testing.T) {
 		test := struct {
-			empty
+			Passing
 			Foo int `tea:"save"`
 		}{
 			Foo: 5,
@@ -77,7 +77,7 @@ func TestLoad(t *testing.T) {
 		}
 
 		var test struct {
-			empty
+			Passing
 			Foo int `tea:"load"`
 		}
 
@@ -95,7 +95,7 @@ func TestLoad(t *testing.T) {
 		}
 
 		var test struct {
-			empty
+			Passing
 			Foo int `tea:"load"`
 		}
 
@@ -110,7 +110,7 @@ func TestLoad(t *testing.T) {
 		}
 
 		var test struct {
-			empty
+			Passing
 			Foo int `tea:"load"`
 		}
 		test.Foo = 5
@@ -131,7 +131,7 @@ func TestMatch(t *testing.T) {
 		}
 
 		var test struct {
-			empty
+			Passing
 			Name string `tea:"match"`
 			Foo  int    `tea:"load"`
 		}
@@ -150,7 +150,7 @@ func TestMatch(t *testing.T) {
 		}
 
 		var test struct {
-			empty
+			Passing
 			Name string `tea:"match"`
 			Foo  int    `tea:"load"`
 		}
@@ -170,7 +170,7 @@ func TestMatch(t *testing.T) {
 		}
 
 		var test struct {
-			empty
+			Passing
 			Name string `tea:"match"`
 			Foo  int    `tea:"load"`
 		}
@@ -199,7 +199,7 @@ func TestMatch(t *testing.T) {
 		}
 
 		var test struct {
-			empty
+			Passing
 			Name string `tea:"match"`
 			Foo  int    `tea:"load"`
 		}

examples/hit-counter/server.go

@@ -12,6 +12,9 @@ type response struct {
 	Hits int  `json:"hits"`
 }
 
+// server implements an http hit-counter server. The hit-count server responds
+// to GET requests with the number of responses it has seen for that path,
+// inclusive of the request itself (i.e., starting at 1).
 type server struct {
 	sync.Mutex
 	counters map[string]int

test.go

@@ -33,12 +33,14 @@ func (f failure) Run(t *testing.T) {
 	t.Error(f.cause.Error())
 }
 
-// empty is an empty test. It does nothing when run, it's just used as a
-// sentinel value to create notes in the test graph and for ... testing the tea
-// package itself.
-type empty struct{}
+// Pass is a Test value that always passes.
+const Pass = Passing("test passed")
 
-func (e empty) Run(t *testing.T) {}
+// Passing is a Test type that always passes. Every value of the Passing type,
+// including the zero value, is a test that will always pass.
+type Passing string
+
+func (p Passing) Run(t *testing.T) {}
 
 // parseName parses the name for a given test
 func parseName(test Test) string {

tree.go

@@ -53,10 +53,10 @@ func exec(t *testing.T, tree *Tree) ([]Test, *env) {
 	history, e := exec(t, tree.parent)
 	test := clone(tree.test)
 	if err := e.load(test); err != nil {
-		// TODO: figure out how to handle load failures like this.
-		panic("load failure: " + err.Error())
+		t.Errorf("test plan failed: %s", err)
+	} else {
+		test.Run(t)
 	}
-	test.Run(t)
 	return append([]Test{test}, history...), e.save(test)
 }