diff --git a/misc/nacl/testzip.proto b/misc/nacl/testzip.proto
index 8e53726ea5..1a3064a477 100644
--- a/misc/nacl/testzip.proto
+++ b/misc/nacl/testzip.proto
@@ -18,6 +18,12 @@ go	src=..
 					asm
 						testdata
 							+
+			doc
+				main.go
+				pkg.go
+				doc_test.go
+				testdata
+					+
 			internal
 				objfile
 					objfile.go
diff --git a/src/cmd/doc/doc_test.go b/src/cmd/doc/doc_test.go
new file mode 100644
index 0000000000..0936d4d2d4
--- /dev/null
+++ b/src/cmd/doc/doc_test.go
@@ -0,0 +1,343 @@
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"os"
+	"os/exec"
+	"regexp"
+	"testing"
+)
+
+const (
+	dataDir = "testdata"
+	binary  = "testdoc"
+)
+
+type test struct {
+	name string
+	args []string // Arguments to "[go] doc".
+	yes  []string // Regular expressions that should match.
+	no   []string // Regular expressions that should not match.
+}
+
+const p = "cmd/doc/testdata"
+
+var tests = []test{
+	// Sanity check.
+	{
+		"fmt",
+		[]string{`fmt`},
+		[]string{`type Formatter interface`},
+		nil,
+	},
+
+	// Package dump includes import, package statement.
+	{
+		"package clause",
+		[]string{p},
+		[]string{`package pkg.*cmd/doc/testdata`},
+		nil,
+	},
+
+	// Constants.
+	// Package dump
+	{
+		"full package",
+		[]string{p},
+		[]string{
+			`Package comment`,
+			`const ExportedConstant = 1`,                            // Simple constant.
+			`ConstOne = 1`,                                          // First entry in constant block.
+			`const ExportedVariable = 1`,                            // Simple variable.
+			`VarOne = 1`,                                            // First entry in variable block.
+			`func ExportedFunc\(a int\) bool`,                       // Function.
+			`type ExportedType struct { ... }`,                      // Exported type.
+			`const ExportedTypedConstant ExportedType = iota`,       // Typed constant.
+			`const ExportedTypedConstant_unexported unexportedType`, // Typed constant, exported for unexported type.
+		},
+		[]string{
+			`const internalConstant = 2`,        // No internal constants.
+			`const internalVariable = 2`,        // No internal variables.
+			`func internalFunc(a int) bool`,     // No internal functions.
+			`Comment about exported constant`,   // No comment for single constant.
+			`Comment about exported variable`,   // No comment for single variable.
+			`Comment about block of constants.`, // No comment for constant block.
+			`Comment about block of variables.`, // No comment for variable block.
+			`Comment before ConstOne`,           // No comment for first entry in constant block.
+			`Comment before VarOne`,             // No comment for first entry in variable block.
+			`ConstTwo = 2`,                      // No second entry in constant block.
+			`VarTwo = 2`,                        // No second entry in variable block.
+			`type unexportedType`,               // No unexported type.
+			`unexportedTypedConstant`,           // No unexported typed constant.
+			`Field`,                             // No fields.
+			`Method`,                            // No methods.
+		},
+	},
+	// Package dump -u
+	{
+		"full package with u",
+		[]string{`-u`, p},
+		[]string{
+			`const ExportedConstant = 1`,      // Simple constant.
+			`const internalConstant = 2`,      // Internal constants.
+			`func internalFunc\(a int\) bool`, // Internal functions.
+		},
+		[]string{
+			`Comment about exported constant`,  // No comment for simple constant.
+			`Comment about block of constants`, // No comment for constant block.
+			`Comment about internal function`,  // No comment for internal function.
+		},
+	},
+
+	// Single constant.
+	{
+		"single constant",
+		[]string{p, `ExportedConstant`},
+		[]string{
+			`Comment about exported constant`, // Include comment.
+			`const ExportedConstant = 1`,
+		},
+		nil,
+	},
+	// Single constant -u.
+	{
+		"single constant with -u",
+		[]string{`-u`, p, `internalConstant`},
+		[]string{
+			`Comment about internal constant`, // Include comment.
+			`const internalConstant = 2`,
+		},
+		nil,
+	},
+	// Block of constants.
+	{
+		"block of constants",
+		[]string{p, `ConstTwo`},
+		[]string{
+			`Comment before ConstOne.\n.*ConstOne = 1`,    // First...
+			`ConstTwo = 2.*Comment on line with ConstTwo`, // And second show up.
+			`Comment about block of constants`,            // Comment does too.
+		},
+		[]string{
+			`constThree`, // No unexported constant.
+		},
+	},
+	// Block of constants -u.
+	{
+		"block of constants with -u",
+		[]string{"-u", p, `constThree`},
+		[]string{
+			`constThree = 3.*Comment on line with constThree`,
+		},
+		nil,
+	},
+
+	// Single variable.
+	{
+		"single variable",
+		[]string{p, `ExportedVariable`},
+		[]string{
+			`ExportedVariable`, // Include comment.
+			`const ExportedVariable = 1`,
+		},
+		nil,
+	},
+	// Single variable -u.
+	{
+		"single variable with -u",
+		[]string{`-u`, p, `internalVariable`},
+		[]string{
+			`Comment about internal variable`, // Include comment.
+			`const internalVariable = 2`,
+		},
+		nil,
+	},
+	// Block of variables.
+	{
+		"block of variables",
+		[]string{p, `VarTwo`},
+		[]string{
+			`Comment before VarOne.\n.*VarOne = 1`,    // First...
+			`VarTwo = 2.*Comment on line with VarTwo`, // And second show up.
+			`Comment about block of variables`,        // Comment does too.
+		},
+		[]string{
+			`varThree= 3`, // No unexported variable.
+		},
+	},
+	// Block of variables -u.
+	{
+		"block of variables with -u",
+		[]string{"-u", p, `varThree`},
+		[]string{
+			`varThree = 3.*Comment on line with varThree`,
+		},
+		nil,
+	},
+
+	// Function.
+	{
+		"function",
+		[]string{p, `ExportedFunc`},
+		[]string{
+			`Comment about exported function`, // Include comment.
+			`func ExportedFunc\(a int\) bool`,
+		},
+		nil,
+	},
+	// Function -u.
+	{
+		"function with -u",
+		[]string{"-u", p, `internalFunc`},
+		[]string{
+			`Comment about internal function`, // Include comment.
+			`func internalFunc\(a int\) bool`,
+		},
+		nil,
+	},
+
+	// Type.
+	{
+		"type",
+		[]string{p, `ExportedType`},
+		[]string{
+			`Comment about exported type`, // Include comment.
+			`type ExportedType struct`,    // Type definition.
+			`Comment before exported field.*\n.*ExportedField +int`,
+			`Has unexported fields`,
+			`func \(ExportedType\) ExportedMethod\(a int\) bool`,
+			`const ExportedTypedConstant ExportedType = iota`, // Must include associated constant.
+		},
+		[]string{
+			`unexportedField`,                // No unexported field.
+			`Comment about exported method.`, // No comment about exported method.
+			`unexportedMethod`,               // No unexported method.
+			`unexportedTypedConstant`,        // No unexported constant.
+		},
+	},
+	// Type -u with unexported fields.
+	{
+		"type with unexported fields and -u",
+		[]string{"-u", p, `ExportedType`},
+		[]string{
+			`Comment about exported type`, // Include comment.
+			`type ExportedType struct`,    // Type definition.
+			`Comment before exported field.*\n.*ExportedField +int`,
+			`unexportedField int.*Comment on line with unexported field.`,
+			`func \(ExportedType\) unexportedMethod\(a int\) bool`,
+			`unexportedTypedConstant`,
+		},
+		[]string{
+			`Has unexported fields`,
+		},
+	},
+	// Unexported type with -u.
+	{
+		"unexported type with -u",
+		[]string{"-u", p, `unexportedType`},
+		[]string{
+			`Comment about unexported type`, // Include comment.
+			`type unexportedType int`,       // Type definition.
+			`func \(unexportedType\) ExportedMethod\(\) bool`,
+			`func \(unexportedType\) unexportedMethod\(\) bool`,
+			`ExportedTypedConstant_unexported unexportedType = iota`,
+			`const unexportedTypedConstant unexportedType = 1`,
+		},
+		nil,
+	},
+
+	// Method.
+	{
+		"method",
+		[]string{p, `ExportedType.ExportedMethod`},
+		[]string{
+			`func \(ExportedType\) ExportedMethod\(a int\) bool`,
+			`Comment about exported method.`,
+		},
+		nil,
+	},
+	// Method  with -u.
+	{
+		"method with -u",
+		[]string{"-u", p, `ExportedType.unexportedMethod`},
+		[]string{
+			`func \(ExportedType\) unexportedMethod\(a int\) bool`,
+			`Comment about unexported method.`,
+		},
+		nil,
+	},
+
+	// Case matching off.
+	{
+		"case matching off",
+		[]string{p, `casematch`},
+		[]string{
+			`CaseMatch`,
+			`Casematch`,
+		},
+		nil,
+	},
+
+	// Case matching on.
+	{
+		"case matching on",
+		[]string{"-c", p, `Casematch`},
+		[]string{
+			`Casematch`,
+		},
+		[]string{
+			`CaseMatch`,
+		},
+	},
+}
+
+func TestDoc(t *testing.T) {
+	for _, test := range tests {
+		var b bytes.Buffer
+		var flagSet flag.FlagSet
+		err := do(&b, &flagSet, test.args)
+		if err != nil {
+			t.Fatalf("%s: %s\n", test.name, err)
+		}
+		output := b.Bytes()
+		failed := false
+		for j, yes := range test.yes {
+			re, err := regexp.Compile(yes)
+			if err != nil {
+				t.Fatalf("%s.%d: compiling %#q: %s", test.name, j, yes, err)
+			}
+			if !re.Match(output) {
+				t.Errorf("%s.%d: no match for %s %#q", test.name, j, test.args, yes)
+				failed = true
+			}
+		}
+		for j, no := range test.no {
+			re, err := regexp.Compile(no)
+			if err != nil {
+				t.Fatalf("%s.%d: compiling %#q: %s", test.name, j, no, err)
+			}
+			if re.Match(output) {
+				t.Errorf("%s.%d: incorrect match for %s %#q", test.name, j, test.args, no)
+				failed = true
+			}
+		}
+		if failed {
+			t.Logf("\n%s", output)
+		}
+	}
+}
+
+// run runs the command, but calls t.Fatal if there is an error.
+func run(c *exec.Cmd, t *testing.T) []byte {
+	output, err := c.CombinedOutput()
+	if err != nil {
+		os.Stdout.Write(output)
+		t.Fatal(err)
+	}
+	return output
+}
diff --git a/src/cmd/doc/main.go b/src/cmd/doc/main.go
index 720b85e902..8d6a0c2fce 100644
--- a/src/cmd/doc/main.go
+++ b/src/cmd/doc/main.go
@@ -30,6 +30,7 @@ import (
 	"flag"
 	"fmt"
 	"go/build"
+	"io"
 	"log"
 	"os"
 	"path"
@@ -40,8 +41,8 @@ import (
 )
 
 var (
-	unexported = flag.Bool("u", false, "show unexported symbols as well as exported")
-	matchCase  = flag.Bool("c", false, "symbol matching honors case (paths not affected)")
+	unexported bool // -u flag
+	matchCase  bool // -c flag
 )
 
 // usage is a replacement usage function for the flags package.
@@ -62,11 +63,36 @@ func usage() {
 func main() {
 	log.SetFlags(0)
 	log.SetPrefix("doc: ")
-	flag.Usage = usage
-	flag.Parse()
-	buildPackage, userPath, symbol := parseArgs()
+	err := do(os.Stdout, flag.CommandLine, os.Args[1:])
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+// do is the workhorse, broken out of main to make testing easier.
+func do(writer io.Writer, flagSet *flag.FlagSet, args []string) (err error) {
+	flagSet.Usage = usage
+	unexported = false
+	matchCase = false
+	flagSet.BoolVar(&unexported, "u", false, "show unexported symbols as well as exported")
+	flagSet.BoolVar(&matchCase, "c", false, "symbol matching honors case (paths not affected)")
+	flagSet.Parse(args)
+	buildPackage, userPath, symbol := parseArgs(flagSet.Args())
 	symbol, method := parseSymbol(symbol)
-	pkg := parsePackage(buildPackage, userPath)
+	pkg := parsePackage(writer, buildPackage, userPath)
+	defer func() {
+		pkg.flush()
+		e := recover()
+		if e == nil {
+			return
+		}
+		pkgError, ok := e.(PackageError)
+		if ok {
+			err = pkgError
+			return
+		}
+		panic(e)
+	}()
 	switch {
 	case symbol == "":
 		pkg.packageDoc()
@@ -76,6 +102,7 @@ func main() {
 	default:
 		pkg.methodDoc(symbol, method)
 	}
+	return nil
 }
 
 // parseArgs analyzes the arguments (if any) and returns the package
@@ -83,8 +110,8 @@ func main() {
 // the path (or "" if it's the current package) and the symbol
 // (possibly with a .method) within that package.
 // parseSymbol is used to analyze the symbol itself.
-func parseArgs() (*build.Package, string, string) {
-	switch flag.NArg() {
+func parseArgs(args []string) (*build.Package, string, string) {
+	switch len(args) {
 	default:
 		usage()
 	case 0:
@@ -94,14 +121,14 @@ func parseArgs() (*build.Package, string, string) {
 		// Done below.
 	case 2:
 		// Package must be importable.
-		pkg, err := build.Import(flag.Arg(0), "", build.ImportComment)
+		pkg, err := build.Import(args[0], "", build.ImportComment)
 		if err != nil {
-			log.Fatal(err)
+			log.Fatalf("%s", err)
 		}
-		return pkg, flag.Arg(0), flag.Arg(1)
+		return pkg, args[0], args[1]
 	}
 	// Usual case: one argument.
-	arg := flag.Arg(0)
+	arg := args[0]
 	// If it contains slashes, it begins with a package path.
 	// First, is it a complete package path as it is? If so, we are done.
 	// This avoids confusion over package paths that have other
@@ -209,7 +236,7 @@ func isIdentifier(name string) {
 // If the unexported flag (-u) is true, isExported returns true because
 // it means that we treat the name as if it is exported.
 func isExported(name string) bool {
-	return *unexported || isUpper(name)
+	return unexported || isUpper(name)
 }
 
 // isUpper reports whether the name starts with an upper case letter.
diff --git a/src/cmd/doc/pkg.go b/src/cmd/doc/pkg.go
index 17ee8cee4f..01268bb52a 100644
--- a/src/cmd/doc/pkg.go
+++ b/src/cmd/doc/pkg.go
@@ -13,6 +13,7 @@ import (
 	"go/format"
 	"go/parser"
 	"go/token"
+	"io"
 	"log"
 	"os"
 	"unicode"
@@ -20,19 +21,36 @@ import (
 )
 
 type Package struct {
-	name     string       // Package name, json for encoding/json.
-	userPath string       // String the user used to find this package.
-	pkg      *ast.Package // Parsed package.
-	file     *ast.File    // Merged from all files in the package
-	doc      *doc.Package
-	build    *build.Package
-	fs       *token.FileSet // Needed for printing.
-	buf      bytes.Buffer
+	writer     io.Writer // Destination for output.
+	name       string    // Package name, json for encoding/json.
+	userPath   string    // String the user used to find this package.
+	unexported bool
+	matchCase  bool
+	pkg        *ast.Package // Parsed package.
+	file       *ast.File    // Merged from all files in the package
+	doc        *doc.Package
+	build      *build.Package
+	fs         *token.FileSet // Needed for printing.
+	buf        bytes.Buffer
+}
+
+type PackageError string // type returned by pkg.Fatalf.
+
+func (p PackageError) Error() string {
+	return string(p)
+}
+
+// pkg.Fatalf is like log.Fatalf, but panics so it can be recovered in the
+// main do function, so it doesn't cause an exit. Allows testing to work
+// without running a subprocess. The log prefix will be added when
+// logged in main; it is not added here.
+func (pkg *Package) Fatalf(format string, args ...interface{}) {
+	panic(PackageError(fmt.Sprintf(format, args...)))
 }
 
 // parsePackage turns the build package we found into a parsed package
 // we can then use to generate documentation.
-func parsePackage(pkg *build.Package, userPath string) *Package {
+func parsePackage(writer io.Writer, pkg *build.Package, userPath string) *Package {
 	fs := token.NewFileSet()
 	// include tells parser.ParseDir which files to include.
 	// That means the file must be in the build package's GoFiles or CgoFiles
@@ -56,7 +74,7 @@ func parsePackage(pkg *build.Package, userPath string) *Package {
 	}
 	// Make sure they are all in one package.
 	if len(pkgs) != 1 {
-		log.Fatalf("multiple packages directory %s", pkg.Dir)
+		log.Fatalf("multiple packages in directory %s", pkg.Dir)
 	}
 	astPkg := pkgs[pkg.Name]
 
@@ -76,6 +94,7 @@ func parsePackage(pkg *build.Package, userPath string) *Package {
 	}
 
 	return &Package{
+		writer:   writer,
 		name:     pkg.Name,
 		userPath: userPath,
 		pkg:      astPkg,
@@ -91,7 +110,7 @@ func (pkg *Package) Printf(format string, args ...interface{}) {
 }
 
 func (pkg *Package) flush() {
-	_, err := os.Stdout.Write(pkg.buf.Bytes())
+	_, err := pkg.writer.Write(pkg.buf.Bytes())
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -391,7 +410,7 @@ func (pkg *Package) symbolDoc(symbol string) {
 // trimUnexportedElems modifies spec in place to elide unexported fields from
 // structs and methods from interfaces (unless the unexported flag is set).
 func trimUnexportedElems(spec *ast.TypeSpec) {
-	if *unexported {
+	if unexported {
 		return
 	}
 	switch typ := spec.Type.(type) {
@@ -450,7 +469,7 @@ func (pkg *Package) printMethodDoc(symbol, method string) bool {
 		if symbol == "" {
 			return false
 		}
-		log.Fatalf("symbol %s is not a type in package %s installed in %q", symbol, pkg.name, pkg.build.ImportPath)
+		pkg.Fatalf("symbol %s is not a type in package %s installed in %q", symbol, pkg.name, pkg.build.ImportPath)
 	}
 	found := false
 	for _, typ := range types {
@@ -470,7 +489,7 @@ func (pkg *Package) printMethodDoc(symbol, method string) bool {
 func (pkg *Package) methodDoc(symbol, method string) {
 	defer pkg.flush()
 	if !pkg.printMethodDoc(symbol, method) {
-		log.Fatalf("no method %s.%s in package %s installed in %q", symbol, method, pkg.name, pkg.build.ImportPath)
+		pkg.Fatalf("no method %s.%s in package %s installed in %q", symbol, method, pkg.name, pkg.build.ImportPath)
 	}
 }
 
@@ -481,7 +500,7 @@ func match(user, program string) bool {
 	if !isExported(program) {
 		return false
 	}
-	if *matchCase {
+	if matchCase {
 		return user == program
 	}
 	for _, u := range user {
diff --git a/src/cmd/doc/testdata/pkg.go b/src/cmd/doc/testdata/pkg.go
new file mode 100644
index 0000000000..ccc2ed64e0
--- /dev/null
+++ b/src/cmd/doc/testdata/pkg.go
@@ -0,0 +1,91 @@
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package comment.
+package pkg
+
+// Constants
+
+// Comment about exported constant.
+const ExportedConstant = 1
+
+// Comment about internal constant.
+const internalConstant = 2
+
+// Comment about block of constants.
+const (
+	// Comment before ConstOne.
+	ConstOne   = 1
+	ConstTwo   = 2 // Comment on line with ConstTwo.
+	constThree = 3 // Comment on line with constThree.
+)
+
+// Variables
+
+// Comment about exported variable.
+const ExportedVariable = 1
+
+// Comment about internal variable.
+const internalVariable = 2
+
+// Comment about block of variables.
+const (
+	// Comment before VarOne.
+	VarOne   = 1
+	VarTwo   = 2 // Comment on line with VarTwo.
+	varThree = 3 // Comment on line with varThree.
+)
+
+// Comment about exported function.
+func ExportedFunc(a int) bool
+
+// Comment about internal function.
+func internalFunc(a int) bool
+
+// Comment about exported type.
+type ExportedType struct {
+	// Comment before exported field.
+	ExportedField   int
+	unexportedField int // Comment on line with unexported field.
+}
+
+// Comment about exported method.
+func (ExportedType) ExportedMethod(a int) bool {
+	return true
+}
+
+// Comment about unexported method.
+func (ExportedType) unexportedMethod(a int) bool {
+	return true
+}
+
+// Constants tied to ExportedType. (The type is a struct so this isn't valid Go,
+// but it parses and that's all we need.)
+const (
+	ExportedTypedConstant ExportedType = iota
+)
+
+const unexportedTypedConstant ExportedType = 1 // In a separate section to test -u.
+
+// Comment about unexported type.
+type unexportedType int
+
+func (unexportedType) ExportedMethod() bool {
+	return true
+}
+
+func (unexportedType) unexportedMethod() bool {
+	return true
+}
+
+// Constants tied to unexportedType.
+const (
+	ExportedTypedConstant_unexported unexportedType = iota
+)
+
+const unexportedTypedConstant unexportedType = 1 // In a separate section to test -u.
+
+// For case matching.
+const CaseMatch = 1
+const Casematch = 2