rework logic and added some test scripts

src/filesystem/interface.js

@@ -209,7 +209,7 @@ function FileSystem(options, callback) {
   //Object that uses filenames as keys
   const statWatchers = new Map();
 
-  this.watchFile = function(filename, options, listener) {
+  this.watchFile = function (filename, options, listener) {
     let prevStat, currStat;
 
     if (Path.isNull(filename)) {
@@ -224,30 +224,39 @@ function FileSystem(options, callback) {
     const interval = options.interval || 5007;
     listener = listener || nop;
 
+    let intervalValue = statWatchers.get(filename);
+
+    // Checks to see if there's a pre-existing watcher on the file
+    if (intervalValue === undefined) {
       // Stores initial prev value to compare 
-    fs.stat(filename, function(err, stats) { 
+      fs.stat(filename, function (err, stats) {
+        var value = setInterval(function () {
+          prevStat = currStat;
+
+          //Conditional check for first run to set initial state for prevStat
+          if(prevStat === undefined) { 
             prevStat = stats;
-      
-      // Stores interval return values
-      statWatchers.set(filename, value);
-      
-      var value = setInterval(function() {
-        fs.stat(filename, function(err, stats) {
-          if(err) {
-            console.log(err);
           } 
-          // Store the current stat
+
           currStat = stats;
-          if(Object.toJSON(prevStat) !== Object.toJSON(currStat)) { 
+
+          if (err) {
+            clearInterval(value);
+            console.warn('[Filer Error] fs.watchFile encountered an error: ' + err);
+          }
+          if (JSON.stringify(prevStat) !== JSON.stringify(currStat)) {
             listener(prevStat, currStat);
           }
           // Set a new prevStat based on previous
           prevStat = currStat;
-        });
         },
         interval
         );
+
+        // Stores interval return values
+        statWatchers.set(filename, value);
       });
+    }
   };
 
   // Deal with various approaches to node ID creation

tests/spec/fs.watchFile.spec.js

@@ -8,24 +8,27 @@ describe('fs.watchFile', function() {
   afterEach(util.cleanup);
 
   it('should be a function', function() {
-    var fs = util.fs();
+    const fs = util.fs();
     expect(typeof fs.watchFile).to.equal('function');
   });
 
-  /*
-  it('should get a change event when writing a file', function(done) {
+  it('should throw an error if a file path is not defined', function() { 
     const fs = util.fs();
     
-    fs.watchFile('/myfile.txt', function(event, filename) {
-      expect(event).to.equal('change');
-      expect(filename).to.equal('/myfile.txt');
-      watcher.close();
-      done();
+    const fn = () => fs.watchFile(undefined);
+    expect(fn).to.throw();
   });
 
-    fs.writeFile('/myfile.txt', 'data', function(error) {
+  it('prev and curr should be populated', function() {
+    const fs = util.fs(); 
+
+    fs.writeFile('/myfile', 'data', function(error) {
       if(error) throw error;
     }); 
+    
+    fs.watchFile('/myfile', function(prev, curr) {
+      expect(prev).to.exist;
+      expect(curr).to.exist;
+    });
   });
-  */
 });