MethodLibraryTest: Implemented an alternative approach that reduces duplicated code and may lead to cleaner tests.

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MOS_MIGRATED_REVID=97326780
diff --git a/src/test/java/com/google/devtools/build/lib/testutil/TestMode.java b/src/test/java/com/google/devtools/build/lib/testutil/TestMode.java
new file mode 100644
index 0000000..5ec7ac2
--- /dev/null
+++ b/src/test/java/com/google/devtools/build/lib/testutil/TestMode.java
@@ -0,0 +1,44 @@
+// Copyright 2015 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 com.google.devtools.build.lib.testutil;
+
+import com.google.devtools.build.lib.events.EventHandler;
+import com.google.devtools.build.lib.rules.SkylarkModules;
+import com.google.devtools.build.lib.syntax.Environment;
+import com.google.devtools.build.lib.syntax.EvaluationContext;
+
+/**
+ * Describes a particular testing mode by determining how the
+ * appropriate {@code EvaluationContext} has to be created
+ */
+public abstract class TestMode {
+  public static final TestMode BUILD = new TestMode() {
+    @Override
+    public EvaluationContext createContext(EventHandler eventHandler, Environment environment)
+        throws Exception {
+      return EvaluationContext.newBuildContext(eventHandler, environment);
+    }
+  };
+
+  public static final TestMode SKYLARK = new TestMode() {
+    @Override
+    public EvaluationContext createContext(EventHandler eventHandler, Environment environment)
+        throws Exception {
+      return SkylarkModules.newEvaluationContext(eventHandler);
+    }
+  };
+
+  public abstract EvaluationContext createContext(
+      EventHandler eventHandler, Environment environment) throws Exception;
+}
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