Turn ProcessWrapperUtil helper functions into a ProcessWrapper class.

This will make it easier to carry the process-wrapper configuration around.
In particular, I want to add the ability to pass arbitrary extra flags to
the tool, and carrying them around explicitly and separately from the
process-wrapper path adds a lot of noise everywhere.

This also cleans up the way we gain access to the process-wrapper binary
and the checks to see if it is supported by homogenizing all logic into
a single place and removing OS-specific checks from a variety of places.

Part of https://github.com/bazelbuild/bazel/issues/10245.

RELNOTES: None.
PiperOrigin-RevId: 310908570
diff --git a/src/test/java/com/google/devtools/build/lib/runtime/ProcessWrapperTest.java b/src/test/java/com/google/devtools/build/lib/runtime/ProcessWrapperTest.java
new file mode 100644
index 0000000..63b0746
--- /dev/null
+++ b/src/test/java/com/google/devtools/build/lib/runtime/ProcessWrapperTest.java
@@ -0,0 +1,98 @@
+// Copyright 2017 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.runtime;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableList;
+import com.google.devtools.build.lib.vfs.FileSystem;
+import com.google.devtools.build.lib.vfs.Path;
+import com.google.devtools.build.lib.vfs.inmemoryfs.InMemoryFileSystem;
+import java.io.IOException;
+import java.time.Duration;
+import java.util.List;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link ProcessWrapper}. */
+@RunWith(JUnit4.class)
+public final class ProcessWrapperTest {
+
+  private FileSystem testFS;
+
+  @Before
+  public void setUp() {
+    testFS = new InMemoryFileSystem();
+  }
+
+  private ProcessWrapper getProcessWrapper(String path) throws IOException {
+    Path processWrapperPath = testFS.getPath(path);
+    processWrapperPath.getParentDirectory().createDirectoryAndParents();
+    processWrapperPath.getOutputStream().close();
+    return new ProcessWrapper(processWrapperPath);
+  }
+
+  @Test
+  public void testProcessWrapperCommandLineBuilder_BuildsWithoutOptionalArguments()
+      throws IOException {
+    ImmutableList<String> commandArguments = ImmutableList.of("echo", "hello, world");
+
+    ImmutableList<String> expectedCommandLine =
+        ImmutableList.<String>builder().add("/some/bin/path").addAll(commandArguments).build();
+
+    ProcessWrapper processWrapper = getProcessWrapper("/some/bin/path");
+    List<String> commandLine = processWrapper.commandLineBuilder(commandArguments).build();
+
+    assertThat(commandLine).containsExactlyElementsIn(expectedCommandLine).inOrder();
+  }
+
+  @Test
+  public void testProcessWrapperCommandLineBuilder_BuildsWithOptionalArguments()
+      throws IOException {
+    ImmutableList<String> commandArguments = ImmutableList.of("echo", "hello, world");
+
+    Duration timeout = Duration.ofSeconds(10);
+    Duration killDelay = Duration.ofSeconds(2);
+    Path stdoutPath = testFS.getPath("/stdout.txt");
+    Path stderrPath = testFS.getPath("/stderr.txt");
+    Path statisticsPath = testFS.getPath("/stats.out");
+
+    ImmutableList<String> expectedCommandLine =
+        ImmutableList.<String>builder()
+            .add("/path/to/process-wrapper")
+            .add("--timeout=" + timeout.getSeconds())
+            .add("--kill_delay=" + killDelay.getSeconds())
+            .add("--stdout=" + stdoutPath)
+            .add("--stderr=" + stderrPath)
+            .add("--stats=" + statisticsPath)
+            .addAll(commandArguments)
+            .build();
+
+    ProcessWrapper processWrapper = getProcessWrapper("/path/to/process-wrapper");
+    List<String> commandLine =
+        processWrapper
+            .commandLineBuilder(commandArguments)
+            .setTimeout(timeout)
+            .setKillDelay(killDelay)
+            .setStdoutPath(stdoutPath)
+            .setStderrPath(stderrPath)
+            .setStatisticsPath(statisticsPath)
+            .build();
+
+    assertThat(commandLine).containsExactlyElementsIn(expectedCommandLine).inOrder();
+  }
+}