diff --git a/src/test/java/com/google/devtools/build/lib/BUILD b/src/test/java/com/google/devtools/build/lib/BUILD
index e8c6f41..051cd77 100644
--- a/src/test/java/com/google/devtools/build/lib/BUILD
+++ b/src/test/java/com/google/devtools/build/lib/BUILD
@@ -489,6 +489,7 @@
         ":windows_testutil",
         "//src/main/java/com/google/devtools/build/lib:os_util",
         "//src/main/java/com/google/devtools/build/lib/clock",
+        "//src/main/java/com/google/devtools/build/lib/shell",
         "//src/main/java/com/google/devtools/build/lib/vfs",
         "//src/main/java/com/google/devtools/build/lib/vfs/inmemoryfs",
         "//src/main/java/com/google/devtools/build/lib/windows",
diff --git a/src/test/java/com/google/devtools/build/lib/windows/WindowsSubprocessTest.java b/src/test/java/com/google/devtools/build/lib/windows/WindowsSubprocessTest.java
new file mode 100644
index 0000000..3d13eff
--- /dev/null
+++ b/src/test/java/com/google/devtools/build/lib/windows/WindowsSubprocessTest.java
@@ -0,0 +1,127 @@
+// Copyright 2016 The Bazel Authors. 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.windows;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableMap;
+import com.google.devtools.build.lib.shell.Subprocess;
+import com.google.devtools.build.lib.shell.SubprocessBuilder;
+import com.google.devtools.build.lib.testutil.TestSpec;
+import com.google.devtools.build.lib.util.OS;
+import com.google.devtools.build.lib.windows.util.WindowsTestUtil;
+
+import java.io.File;
+import java.nio.charset.Charset;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Unit tests for {@link WindowsSubprocess}.
+ */
+@RunWith(JUnit4.class)
+@TestSpec(localOnly = true, supportedOs = OS.WINDOWS)
+public class WindowsSubprocessTest {
+  private static final Charset UTF8 = Charset.forName("UTF-8");
+  private String mockSubprocess;
+  private String mockBinary;
+  private Subprocess process;
+
+  @Before
+  public void loadJni() throws Exception {
+    mockSubprocess = WindowsTestUtil.getRunfile(
+        "io_bazel/src/test/java/com/google/devtools/build/lib/MockSubprocess_deploy.jar");
+    mockBinary = System.getProperty("java.home") + "\\bin\\java.exe";
+
+    process = null;
+  }
+
+  @After
+  public void terminateProcess() throws Exception {
+    if (process != null) {
+      process.destroy();
+      process.close();
+      process = null;
+    }
+  }
+
+  @Test
+  public void testSystemRootIsSetByDefault() throws Exception {
+    SubprocessBuilder subprocessBuilder = new SubprocessBuilder();
+    subprocessBuilder.setWorkingDirectory(new File("."));
+    subprocessBuilder.setSubprocessFactory(WindowsSubprocessFactory.INSTANCE);
+    subprocessBuilder.setArgv(mockBinary, "-jar", mockSubprocess, "O$SYSTEMROOT");
+    process = subprocessBuilder.start();
+    process.waitFor();
+    assertThat(process.exitValue()).isEqualTo(0);
+
+    byte[] buf = new byte[11];
+    process.getInputStream().read(buf);
+    assertThat(new String(buf, UTF8).trim()).isEqualTo(System.getenv("SYSTEMROOT").trim());
+  }
+
+  @Test
+  public void testSystemDriveIsSetByDefault() throws Exception {
+    SubprocessBuilder subprocessBuilder = new SubprocessBuilder();
+    subprocessBuilder.setWorkingDirectory(new File("."));
+    subprocessBuilder.setSubprocessFactory(WindowsSubprocessFactory.INSTANCE);
+    subprocessBuilder.setArgv(mockBinary, "-jar", mockSubprocess, "O$SYSTEMDRIVE");
+    process = subprocessBuilder.start();
+    process.waitFor();
+    assertThat(process.exitValue()).isEqualTo(0);
+
+    byte[] buf = new byte[3];
+    process.getInputStream().read(buf);
+    assertThat(new String(buf, UTF8).trim()).isEqualTo(System.getenv("SYSTEMDRIVE").trim());
+  }
+
+  @Test
+  public void testSystemRootIsSet() throws Exception {
+    SubprocessBuilder subprocessBuilder = new SubprocessBuilder();
+    subprocessBuilder.setWorkingDirectory(new File("."));
+    subprocessBuilder.setSubprocessFactory(WindowsSubprocessFactory.INSTANCE);
+    subprocessBuilder.setArgv(mockBinary, "-jar", mockSubprocess, "O$SYSTEMROOT");
+    // Case shouldn't matter on Windows
+    subprocessBuilder.setEnv(ImmutableMap.of("SystemRoot", "C:\\MySystemRoot"));
+    process = subprocessBuilder.start();
+    process.waitFor();
+    assertThat(process.exitValue()).isEqualTo(0);
+
+    byte[] buf = new byte[16];
+    process.getInputStream().read(buf);
+    assertThat(new String(buf, UTF8).trim()).isEqualTo("C:\\MySystemRoot");
+  }
+
+  @Test
+  public void testSystemDriveIsSet() throws Exception {
+    SubprocessBuilder subprocessBuilder = new SubprocessBuilder();
+    subprocessBuilder.setWorkingDirectory(new File("."));
+    subprocessBuilder.setSubprocessFactory(WindowsSubprocessFactory.INSTANCE);
+    subprocessBuilder.setArgv(mockBinary, "-jar", mockSubprocess, "O$SYSTEMDRIVE");
+    // Case shouldn't matter on Windows
+    subprocessBuilder.setEnv(ImmutableMap.of("SystemDrive", "X:"));
+    process = subprocessBuilder.start();
+    process.waitFor();
+    assertThat(process.exitValue()).isEqualTo(0);
+
+    byte[] buf = new byte[3];
+    process.getInputStream().read(buf);
+    assertThat(new String(buf, UTF8).trim()).isEqualTo("X:");
+  }
+}