diff --git a/Android.bp b/Android.bp
index 37be36c..29ad569 100644
--- a/Android.bp
+++ b/Android.bp
@@ -255,6 +255,7 @@
     ],
     testSrcs: [
         "java/app_test.go",
+        "java/dexpreopt_test.go",
         "java/java_test.go",
         "java/jdeps_test.go",
     ],
diff --git a/android/testing.go b/android/testing.go
index ca7e7ce..d318839 100644
--- a/android/testing.go
+++ b/android/testing.go
@@ -121,33 +121,59 @@
 	ctx.Context.MockFileSystem(files)
 }
 
+// TestingModule is wrapper around an android.Module that provides methods to find information about individual
+// ctx.Build parameters for verification in tests.
 type TestingModule struct {
 	module Module
 }
 
+// Module returns the Module wrapped by the TestingModule.
 func (m TestingModule) Module() Module {
 	return m.module
 }
 
-func (m TestingModule) Rule(rule string) BuildParams {
+// MaybeRule finds a call to ctx.Build with BuildParams.Rule set to a rule with the given name.  Returns an empty
+// BuildParams if no rule is found.
+func (m TestingModule) MaybeRule(rule string) BuildParams {
 	for _, p := range m.module.BuildParamsForTests() {
 		if strings.Contains(p.Rule.String(), rule) {
 			return p
 		}
 	}
-	panic(fmt.Errorf("couldn't find rule %q", rule))
+	return BuildParams{}
 }
 
-func (m TestingModule) Description(desc string) BuildParams {
+// Rule finds a call to ctx.Build with BuildParams.Rule set to a rule with the given name.  Panics if no rule is found.
+func (m TestingModule) Rule(rule string) BuildParams {
+	p := m.MaybeRule(rule)
+	if p.Rule == nil {
+		panic(fmt.Errorf("couldn't find rule %q", rule))
+	}
+	return p
+}
+
+// MaybeDescription finds a call to ctx.Build with BuildParams.Description set to a the given string.  Returns an empty
+// BuildParams if no rule is found.
+func (m TestingModule) MaybeDescription(desc string) BuildParams {
 	for _, p := range m.module.BuildParamsForTests() {
 		if p.Description == desc {
 			return p
 		}
 	}
-	panic(fmt.Errorf("couldn't find description %q", desc))
+	return BuildParams{}
 }
 
-func (m TestingModule) Output(file string) BuildParams {
+// Description finds a call to ctx.Build with BuildParams.Description set to a the given string.  Panics if no rule is
+// found.
+func (m TestingModule) Description(desc string) BuildParams {
+	p := m.MaybeDescription(desc)
+	if p.Rule == nil {
+		panic(fmt.Errorf("couldn't find description %q", desc))
+	}
+	return p
+}
+
+func (m TestingModule) maybeOutput(file string) (BuildParams, []string) {
 	var searchedOutputs []string
 	for _, p := range m.module.BuildParamsForTests() {
 		outputs := append(WritablePaths(nil), p.Outputs...)
@@ -156,13 +182,30 @@
 		}
 		for _, f := range outputs {
 			if f.String() == file || f.Rel() == file {
-				return p
+				return p, nil
 			}
 			searchedOutputs = append(searchedOutputs, f.Rel())
 		}
 	}
-	panic(fmt.Errorf("couldn't find output %q.\nall outputs: %v",
-		file, searchedOutputs))
+	return BuildParams{}, searchedOutputs
+}
+
+// MaybeOutput finds a call to ctx.Build with a BuildParams.Output or BuildParams.Outputspath whose String() or Rel()
+// value matches the provided string.  Returns an empty BuildParams if no rule is found.
+func (m TestingModule) MaybeOutput(file string) BuildParams {
+	p, _ := m.maybeOutput(file)
+	return p
+}
+
+// Output finds a call to ctx.Build with a BuildParams.Output or BuildParams.Outputspath whose String() or Rel()
+// value matches the provided string.  Panics if no rule is found.
+func (m TestingModule) Output(file string) BuildParams {
+	p, searchedOutputs := m.maybeOutput(file)
+	if p.Rule == nil {
+		panic(fmt.Errorf("couldn't find output %q.\nall outputs: %v",
+			file, searchedOutputs))
+	}
+	return p
 }
 
 func FailIfErrored(t *testing.T, errs []error) {
diff --git a/java/dexpreopt_test.go b/java/dexpreopt_test.go
new file mode 100644
index 0000000..5b55799
--- /dev/null
+++ b/java/dexpreopt_test.go
@@ -0,0 +1,126 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import (
+	"testing"
+)
+
+func TestDexpreoptEnabled(t *testing.T) {
+	tests := []struct {
+		name    string
+		bp      string
+		enabled bool
+	}{
+		{
+			name: "app",
+			bp: `
+				android_app {
+					name: "foo",
+					srcs: ["a.java"],
+				}`,
+			enabled: true,
+		},
+		{
+			name: "installable java library",
+			bp: `
+				java_library {
+					name: "foo",
+					installable: true,
+					srcs: ["a.java"],
+				}`,
+			enabled: true,
+		},
+		{
+			name: "java binary",
+			bp: `
+				java_binary {
+					name: "foo",
+					srcs: ["a.java"],
+				}`,
+			enabled: true,
+		},
+
+		{
+			name: "app without sources",
+			bp: `
+				android_app {
+					name: "foo",
+				}`,
+			// TODO(ccross): this should probably be false
+			enabled: true,
+		},
+		{
+			name: "installable java library without sources",
+			bp: `
+				java_library {
+					name: "foo",
+					installable: true,
+				}`,
+			// TODO(ccross): this should probably be false
+			enabled: true,
+		},
+
+		{
+			name: "static java library",
+			bp: `
+				java_library {
+					name: "foo",
+					srcs: ["a.java"],
+				}`,
+			enabled: false,
+		},
+		{
+			name: "android test",
+			bp: `
+				android_test {
+					name: "foo",
+					srcs: ["a.java"],
+				}`,
+			enabled: false,
+		},
+		{
+			name: "android test helper app",
+			bp: `
+				android_test_helper_app {
+					name: "foo",
+					srcs: ["a.java"],
+				}`,
+			enabled: false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ctx := testJava(t, test.bp)
+
+			dexpreopt := ctx.ModuleForTests("foo", "android_common").MaybeDescription("dexpreopt")
+			enabled := dexpreopt.Rule != nil
+
+			if enabled != test.enabled {
+				t.Fatalf("want dexpreopt %s, got %s", enabledString(test.enabled), enabledString(enabled))
+			}
+		})
+
+	}
+}
+
+func enabledString(enabled bool) string {
+	if enabled {
+		return "enabled"
+	} else {
+		return "disabled"
+	}
+}
diff --git a/java/java_test.go b/java/java_test.go
index 2a54f69..c4cf905 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -76,9 +76,12 @@
 	ctx.RegisterModuleType("android_app", android.ModuleFactoryAdaptor(AndroidAppFactory))
 	ctx.RegisterModuleType("android_library", android.ModuleFactoryAdaptor(AndroidLibraryFactory))
 	ctx.RegisterModuleType("android_test", android.ModuleFactoryAdaptor(AndroidTestFactory))
+	ctx.RegisterModuleType("android_test_helper_app", android.ModuleFactoryAdaptor(AndroidTestHelperAppFactory))
+	ctx.RegisterModuleType("java_binary", android.ModuleFactoryAdaptor(BinaryFactory))
 	ctx.RegisterModuleType("java_binary_host", android.ModuleFactoryAdaptor(BinaryHostFactory))
 	ctx.RegisterModuleType("java_library", android.ModuleFactoryAdaptor(LibraryFactory))
 	ctx.RegisterModuleType("java_library_host", android.ModuleFactoryAdaptor(LibraryHostFactory))
+	ctx.RegisterModuleType("java_test", android.ModuleFactoryAdaptor(TestFactory))
 	ctx.RegisterModuleType("java_import", android.ModuleFactoryAdaptor(ImportFactory))
 	ctx.RegisterModuleType("java_defaults", android.ModuleFactoryAdaptor(defaultsFactory))
 	ctx.RegisterModuleType("java_system_modules", android.ModuleFactoryAdaptor(SystemModulesFactory))