diff --git a/config/travis.js b/config/travis.js
index 3db40e8..cede169 100644
--- a/config/travis.js
+++ b/config/travis.js
@@ -1,24 +1,8 @@
 // @flow
 
-const chalk = require("chalk");
-const child_process = require("child_process");
+const execDependencyGraph = require("../src/tools/execDependencyGraph");
 
-/*::
-type TaskId = string;
-type Task = {|
-  +id: TaskId,
-  +cmd: $ReadOnlyArray<string>,
-  +deps: $ReadOnlyArray<TaskId>,
-|};
-
-type TaskResult = {|
-  +id: TaskId,
-  +success: boolean,
-  +status: number,
-  +stdout: string,
-  +stderr: string,
-|};
-*/
+main();
 
 function main() {
   const mode =
@@ -26,170 +10,8 @@ function main() {
     process.argv.includes("--full")
       ? "FULL"
       : "BASIC";
-  processAll(makeTasks(mode));
-}
-main();
-
-async function processAll(tasks /*: $ReadOnlyArray<Task> */) {
-  const tasksById /*: {[TaskId]: Task} */ = {};
-  tasks.forEach((task) => {
-    if (tasksById[task.id] !== undefined) {
-      throw new Error("Duplicate tasks with ID: " + task.id);
-    }
-    tasksById[task.id] = task;
-  });
-
-  const completedTasks /*: Map<TaskId, TaskResult> */ = new Map();
-  const tasksInProgress /*: Map<TaskId, Promise<TaskResult>> */ = new Map();
-  const remainingTasks /*: Set<TaskId> */ = new Set(Object.keys(tasksById));
-
-  function spawnTasksWhoseDependenciesHaveCompleted() {
-    for (const task of tasks) {
-      if (!remainingTasks.has(task.id)) {
-        continue;
-      }
-      if (incompleteDependencies(task).length > 0) {
-        continue;
-      }
-      // Ready to spawn!
-      remainingTasks.delete(task.id);
-      console.log(chalk.bgBlue.bold.white("  GO  ") + " " + task.id);
-      tasksInProgress.set(task.id, processOne(task));
-    }
-  }
-
-  function incompleteDependencies(task /*: Task */) /*: TaskId[] */ {
-    return task.deps.filter((dep) => {
-      const result = completedTasks.get(dep);
-      return !(result && result.success);
-    });
-  }
-
-  async function awaitAnyTask() {
-    if (tasksInProgress.size === 0) {
-      throw new Error("Invariant violation: No tasks to wait for.");
-    }
-    const result /*: TaskResult */ = await Promise.race(
-      Array.from(tasksInProgress.values())
-    );
-    tasksInProgress.delete(result.id);
-    completedTasks.set(result.id, result);
-    displayResult(result.id, result, "OVERVIEW");
-  }
-
-  function displayResult(
-    id /*: TaskId */,
-    result /*: ?TaskResult */,
-    mode /*: "OVERVIEW" | "FULL" */
-  ) {
-    const success = result && result.success;
-    const badge = success
-      ? chalk.bgGreen.bold.white(" PASS ")
-      : chalk.bgRed.bold.white(" FAIL ");
-    console.log(`${badge} ${id}`);
-
-    if (mode === "OVERVIEW" && success) {
-      return;
-    }
-
-    let loggedAnything = false;
-    function log(...args) {
-      console.log(...args);
-      loggedAnything = true;
-    }
-    if (!result) {
-      log(`Did not run. Missing dependencies:`);
-      incompleteDependencies(tasksById[id]).forEach((dep) => {
-        log(`  - ${dep}`);
-      });
-      log();
-      return;
-    }
-    if (result.status !== 0) {
-      log("Exit code: " + result.status);
-    }
-    if (result.stdout.length > 0) {
-      log("Contents of stdout:");
-      displayOutputStream(result.stdout);
-    }
-    if (result.stderr.length > 0) {
-      log("Contents of stderr:");
-      displayOutputStream(result.stderr);
-    }
-    if (loggedAnything) {
-      console.log();
-    }
-  }
-
-  function displayOutputStream(streamContents /*: string */) {
-    streamContents.split("\n").forEach((line, index, array) => {
-      if (line === "" && index === array.length - 1) {
-        return;
-      } else {
-        console.log("    " + line);
-      }
-    });
-  }
-
-  function printSection(name /*: string */) {
-    console.log("\n" + chalk.bold(name));
-  }
-
-  printSection("Starting tasks");
-  spawnTasksWhoseDependenciesHaveCompleted();
-  while (tasksInProgress.size > 0) {
-    await awaitAnyTask();
-    spawnTasksWhoseDependenciesHaveCompleted();
-  }
-
-  if (remainingTasks.size > 0) {
-    printSection("Unreachable tasks");
-    Array.from(remainingTasks.values()).forEach((line) => {
-      console.log(`  - ${line}`);
-    });
-  }
-
-  printSection("Full results");
-  for (const task of tasks) {
-    const result = completedTasks.get(task.id);
-    displayResult(task.id, result, "FULL");
-  }
-
-  printSection("Overview");
-  const failedTasks = tasks.map((t) => t.id).filter((id) => {
-    const result = completedTasks.get(id);
-    return !result || !result.success;
-  });
-  if (failedTasks.length > 0) {
-    console.log("Failed tasks:");
-    failedTasks.forEach((line) => {
-      console.log(`  - ${line}`);
-    });
-  }
-  const overallSuccess /*: boolean */ = failedTasks.length === 0;
-  const overallBadge = overallSuccess
-    ? chalk.bgGreen.bold.white(" SUCCESS ")
-    : chalk.bgRed.bold.white(" FAILURE ");
-  console.log("Final result: " + overallBadge);
-  process.exitCode = overallSuccess ? 0 : 1;
-}
-
-function processOne(task /*: Task */) /*: Promise<TaskResult> */ {
-  if (task.cmd.length === 0) {
-    throw new Error("Empty command for task: " + task.id);
-  }
-  const file = task.cmd[0];
-  const args = task.cmd.slice(1);
-  return new Promise((resolve, _unused_reject) => {
-    child_process.execFile(file, args, (error, stdout, stderr) => {
-      resolve({
-        id: task.id,
-        success: !error,
-        status: error ? error.code : 0,
-        stdout: stdout.toString(),
-        stderr: stderr.toString(),
-      });
-    });
+  execDependencyGraph(makeTasks(mode)).then(({success}) => {
+    process.exitCode = success ? 0 : 1;
   });
 }
 
diff --git a/src/tools/execDependencyGraph.js b/src/tools/execDependencyGraph.js
new file mode 100644
index 0000000..d642439
--- /dev/null
+++ b/src/tools/execDependencyGraph.js
@@ -0,0 +1,194 @@
+// @flow
+
+// NOTE: This module must be written in vanilla ECMAScript that can be
+// run by Node without a preprocessor. That means that we use
+// `module.exports` and `require` instead of ECMAScript module keywords,
+// and we use the Flow comment syntax instead of the inline syntax.
+
+const chalk = require("chalk");
+const child_process = require("child_process");
+
+/*::
+type TaskId = string;
+type Task = {|
+  +id: TaskId,
+  +cmd: $ReadOnlyArray<string>,
+  +deps: $ReadOnlyArray<TaskId>,
+|};
+
+type TaskResult = {|
+  +id: TaskId,
+  +success: boolean,
+  +status: number,
+  +stdout: string,
+  +stderr: string,
+|};
+type OverallResult = {|
+  +success: boolean,
+|};
+*/
+
+module.exports = async function execDepgraph(
+  tasks /*: $ReadOnlyArray<Task> */
+) /*: Promise<OverallResult> */ {
+  const tasksById /*: {[TaskId]: Task} */ = {};
+  tasks.forEach((task) => {
+    if (tasksById[task.id] !== undefined) {
+      throw new Error("Duplicate tasks with ID: " + task.id);
+    }
+    tasksById[task.id] = task;
+  });
+
+  const completedTasks /*: Map<TaskId, TaskResult> */ = new Map();
+  const tasksInProgress /*: Map<TaskId, Promise<TaskResult>> */ = new Map();
+  const remainingTasks /*: Set<TaskId> */ = new Set(Object.keys(tasksById));
+
+  function spawnTasksWhoseDependenciesHaveCompleted() {
+    for (const task of tasks) {
+      if (!remainingTasks.has(task.id)) {
+        continue;
+      }
+      if (incompleteDependencies(task).length > 0) {
+        continue;
+      }
+      // Ready to spawn!
+      remainingTasks.delete(task.id);
+      console.log(chalk.bgBlue.bold.white("  GO  ") + " " + task.id);
+      tasksInProgress.set(task.id, processTask(task));
+    }
+  }
+
+  function incompleteDependencies(task /*: Task */) /*: TaskId[] */ {
+    return task.deps.filter((dep) => {
+      const result = completedTasks.get(dep);
+      return !(result && result.success);
+    });
+  }
+
+  async function awaitAnyTask() {
+    if (tasksInProgress.size === 0) {
+      throw new Error("Invariant violation: No tasks to wait for.");
+    }
+    const result /*: TaskResult */ = await Promise.race(
+      Array.from(tasksInProgress.values())
+    );
+    tasksInProgress.delete(result.id);
+    completedTasks.set(result.id, result);
+    displayResult(result.id, result, "OVERVIEW");
+  }
+
+  function displayResult(
+    id /*: TaskId */,
+    result /*: ?TaskResult */,
+    mode /*: "OVERVIEW" | "FULL" */
+  ) {
+    const success = result && result.success;
+    const badge = success
+      ? chalk.bgGreen.bold.white(" PASS ")
+      : chalk.bgRed.bold.white(" FAIL ");
+    console.log(`${badge} ${id}`);
+
+    if (mode === "OVERVIEW" && success) {
+      return;
+    }
+
+    let loggedAnything = false;
+    function log(...args) {
+      console.log(...args);
+      loggedAnything = true;
+    }
+    if (!result) {
+      log(`Did not run. Missing dependencies:`);
+      incompleteDependencies(tasksById[id]).forEach((dep) => {
+        log(`  - ${dep}`);
+      });
+      log();
+      return;
+    }
+    if (result.status !== 0) {
+      log("Exit code: " + result.status);
+    }
+    if (result.stdout.length > 0) {
+      log("Contents of stdout:");
+      displayOutputStream(result.stdout);
+    }
+    if (result.stderr.length > 0) {
+      log("Contents of stderr:");
+      displayOutputStream(result.stderr);
+    }
+    if (loggedAnything) {
+      console.log();
+    }
+  }
+
+  function displayOutputStream(streamContents /*: string */) {
+    streamContents.split("\n").forEach((line, index, array) => {
+      if (line === "" && index === array.length - 1) {
+        return;
+      } else {
+        console.log("    " + line);
+      }
+    });
+  }
+
+  function printSection(name /*: string */) {
+    console.log("\n" + chalk.bold(name));
+  }
+
+  printSection("Starting tasks");
+  spawnTasksWhoseDependenciesHaveCompleted();
+  while (tasksInProgress.size > 0) {
+    await awaitAnyTask();
+    spawnTasksWhoseDependenciesHaveCompleted();
+  }
+
+  if (remainingTasks.size > 0) {
+    printSection("Unreachable tasks");
+    Array.from(remainingTasks.values()).forEach((line) => {
+      console.log(`  - ${line}`);
+    });
+  }
+
+  printSection("Full results");
+  for (const task of tasks) {
+    const result = completedTasks.get(task.id);
+    displayResult(task.id, result, "FULL");
+  }
+
+  printSection("Overview");
+  const failedTasks = tasks.map((t) => t.id).filter((id) => {
+    const result = completedTasks.get(id);
+    return !result || !result.success;
+  });
+  if (failedTasks.length > 0) {
+    console.log("Failed tasks:");
+    failedTasks.forEach((line) => {
+      console.log(`  - ${line}`);
+    });
+  }
+  const overallSuccess /*: boolean */ = failedTasks.length === 0;
+  const overallBadge = overallSuccess
+    ? chalk.bgGreen.bold.white(" SUCCESS ")
+    : chalk.bgRed.bold.white(" FAILURE ");
+  console.log("Final result: " + overallBadge);
+  return Promise.resolve({success: overallSuccess});
+};
+
+function processTask(task /*: Task */) /*: Promise<TaskResult> */ {
+  if (task.cmd.length === 0) {
+    throw new Error("Empty command for task: " + task.id);
+  }
+  const file = task.cmd[0];
+  const args = task.cmd.slice(1);
+  return new Promise((resolve, _unused_reject) => {
+    child_process.execFile(file, args, (error, stdout, stderr) => {
+      resolve({
+        id: task.id,
+        success: !error,
+        status: error ? error.code : 0,
+        stdout: stdout.toString(),
+        stderr: stderr.toString(),
+      });
+    });
+  });
+}