Fix 'gulp watch' command and also allow compilation of test files. (#672)

The compilation results of the test files are discarded... the process
is just to allow the typescript compiler to pass over all files at once
(rather than encountering errors one file at a time by running unit
tests.)

Author: rsgowman

gulpfile.js

@@ -37,7 +37,12 @@ var replace = require('gulp-replace');
 /****************/
 var paths = {
   src: [
-    'src/**/*.ts'
+    'src/**/*.ts',
+  ],
+
+  test: [
+    'test/**/*.ts',
+    '!test/integration/typescript/src/example*.ts',
   ],
 
   databaseSrc: [
@@ -52,6 +57,8 @@ var paths = {
 // rather than including both src and test in the lib dir.
 var buildProject = ts.createProject('tsconfig.json', {rootDir: 'src'});
 
+var buildTest = ts.createProject('tsconfig.json');
+
 var banner = `/*! firebase-admin v${pkg.version} */\n`;
 
 /***********/
@@ -79,6 +86,16 @@ gulp.task('compile', function() {
     .pipe(gulp.dest(paths.build))
 });
 
+/**
+ * Task only used to capture typescript compilation errors in the test suite.
+ * Output is discarded.
+ */
+gulp.task('compile_test', function() {
+  return gulp.src(paths.test)
+    // Compile Typescript into .js and .d.ts files
+    .pipe(buildTest())
+});
+
 gulp.task('copyDatabase', function() {
   return gulp.src(paths.databaseSrc)
     // Add headers
@@ -98,9 +115,11 @@ gulp.task('copyTypings', function() {
     .pipe(gulp.dest(paths.build))
 });
 
+gulp.task('compile_all', gulp.series('compile', 'copyDatabase', 'copyTypings', 'compile_test'));
+
 // Regenerates js every time a source file changes
 gulp.task('watch', function() {
-  gulp.watch(paths.src, ['compile']);
+  gulp.watch(paths.src.concat(paths.test), {ignoreInitial: false}, gulp.series('compile_all'));
 });
 
 // Build task