diff --git a/test/read.test.js b/test/read.test.js
index 98e3b92..3b49978 100644
--- a/test/read.test.js
+++ b/test/read.test.js
@@ -139,10 +139,15 @@ test('read from fd', t => {
       flags: 'r'
     })
     .then(fd => {
-      return file.read(fd).then(result => {
-        t.equal(result.toString(), 'Hi!!!\n');
-        return file.close(fd);
-      });
+      return file
+        .read(fd, {
+          length: 3
+        })
+        .then(result => {
+          t.equal(result.toString(), 'Hi!');
+          return file.close(fd);
+        })
+        .then(t.end);
     })
     .catch(error => {
       t.error(error);
diff --git a/test/readfile.test.js b/test/readfile.test.js
index 43589c6..9fb4844 100644
--- a/test/readfile.test.js
+++ b/test/readfile.test.js
@@ -43,6 +43,26 @@ test('readFile utf8', t => {
     });
 });
 
+test('readFile from fd', t => {
+  file
+    .open(filepath1, {
+      flags: 'r'
+    })
+    .then(fd => {
+      return file
+        .readFile(fd)
+        .then(result => {
+          t.equal(result.toString(), '0123456789\n');
+          return file.close(fd);
+        })
+        .then(t.end);
+    })
+    .catch(error => {
+      t.error(error);
+      t.end();
+    });
+});
+
 test('readFile non-existing file', t => {
   const path = resolve(__dirname, './data/nothing-here.txt');
 
diff --git a/test/truncate.test.js b/test/truncate.test.js
index 6416acd..40bcd95 100644
--- a/test/truncate.test.js
+++ b/test/truncate.test.js
@@ -29,6 +29,30 @@ test('truncate', t => {
     });
 });
 
+test('truncate with fd', t => {
+  file
+    .open(filepath1, {
+      flags: 'r+'
+    })
+    .then(fd => {
+      return file
+        .truncate(fd, {
+          length: 8
+        })
+        .then(() => {
+          const text = readFileSync(filepath1, 'utf8');
+          t.equal(text.length, 8, 'text.length is 8');
+          t.equal(text, 'abcdefgh');
+          return file.close(fd);
+        })
+        .then(t.end);
+    })
+    .catch(error => {
+      t.error(error);
+      t.end();
+    });
+});
+
 test('truncate all', t => {
   file
     .truncate(filepath1)
diff --git a/test/writefile.test.js b/test/writefile.test.js
index 0147675..2eb7f34 100644
--- a/test/writefile.test.js
+++ b/test/writefile.test.js
@@ -65,6 +65,26 @@ test('writeFile to a new directory', t => {
     });
 });
 
+test('readFile to fd', t => {
+  file
+    .open(file4, {
+      flags: 'r+'
+    })
+    .then(fd => {
+      return file
+        .writeFile(fd, '_ an old')
+        .then(() => {
+          t.equal(readFileSync(file4, 'utf8'), '_ an old directory');
+          return file.close(fd);
+        })
+        .then(t.end);
+    })
+    .catch(error => {
+      t.error(error);
+      t.end();
+    });
+});
+
 test('writeFile error', t => {
   file
     .writeFile()