test: refactor error checks to use assert.ifError/mustSucceed

Replace manual `if (err) assert.fail(err)` and `assert.ok(!err)` with
`assert.ifError()` or `common.mustSucceed()` in a few tests to clarify
intent and follow project conventions.

- test/parallel/test-child-process-send-returns-boolean.js
- test/parallel/test-dgram-blocklist.js
- test/parallel/test-fs-watchfile.js

Author: KimSH39

test/parallel/test-child-process-send-returns-boolean.js

@@ -33,19 +33,19 @@ const subScript = fixtures.path('child-process-persistent.js');
 
     // Sending a handle and not giving the tickQueue time to acknowledge should
     // create the internal backlog, but leave it empty.
-    const rv1 = s.send('one', handle, (err) => { if (err) assert.fail(err); });
+    const rv1 = s.send('one', handle, assert.ifError);
     assert.strictEqual(rv1, true);
     // Since the first `send` included a handle (should be unacknowledged),
     // we can safely queue up only one more message.
-    const rv2 = s.send('two', (err) => { if (err) assert.fail(err); });
+    const rv2 = s.send('two', assert.ifError);
     assert.strictEqual(rv2, true);
     // The backlog should now be indicate to backoff.
-    const rv3 = s.send('three', (err) => { if (err) assert.fail(err); });
+    const rv3 = s.send('three', assert.ifError);
     assert.strictEqual(rv3, false);
     const rv4 = s.send('four', (err) => {
-      if (err) assert.fail(err);
+      assert.ifError(err);
       // `send` queue should have been drained.
-      const rv5 = s.send('5', handle, (err) => { if (err) assert.fail(err); });
+      const rv5 = s.send('5', handle, assert.ifError);
       assert.strictEqual(rv5, true);
 
       // End test and cleanup.

test/parallel/test-dgram-blocklist.js

@@ -41,9 +41,13 @@ const net = require('net');
   receiveSocket.bind(0, common.localhostIPv4, common.mustCall(() => {
     const addressInfo = receiveSocket.address();
     const client = dgram.createSocket('udp4');
-    client.send('hello', addressInfo.port, addressInfo.address, common.mustCall((err) => {
-      assert.ok(!err);
-      client.close();
-    }));
+    client.send(
+      'hello',
+      addressInfo.port,
+      addressInfo.address,
+      common.mustSucceed(() => {
+        client.close();
+      })
+    );
   }));
 }

test/parallel/test-fs-watchfile.js

@@ -94,9 +94,7 @@ if (common.isLinux || common.isMacOS || common.isWindows) {
     }));
 
     const interval = setInterval(() => {
-      fs.writeFile(path.join(dir, 'foo.txt'), 'foo', common.mustCall((err) => {
-        if (err) assert.fail(err);
-      }));
+      fs.writeFile(path.join(dir, 'foo.txt'), 'foo', common.mustSucceed());
     }, 1);
   }