# \[Go\] \[Stage #QP2\] Builtin Command Autocompletion works Locally but fails in tests

**URL:** <https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520>\
**Category:** Challenges\
**Tags:** challenge:shell\
**Created:** [March 11, 2025, 6:04pm UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520 "2025-03-11T18:04:04Z")\
**Posts on this page:** 10\
**Page:** 1

<div class="post-metadata">

**Author:** ![dgiridharan](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/dgiridharan/32/6534_2.png) [@dgiridharan](https://forum.codecrafters.io/u/dgiridharan)\
**Post date:** [March 11, 2025, 6:04pm UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/1 "2025-03-11T18:04:04Z")

</div>

### Info

**Challenge:** Build your own shell  
**Language:** Go  
**Stage:** #QP2 - Builtin completions

### Context/Issue

I’m currently working on the “Build Your Own Shell” challenge in Go. Locally, my autocompletion works flawlessly, but CodeCrafters’ tests keep failing.

Interestingly, after my latest changes, running `codecrafters test --previous` started failing. However, everything still works fine in my local environment.

### Logs

Output from `codecrafters test --previous`

```auto
[compile] Moved ./.codecrafters/run.sh → ./your_program.sh
[compile] Compilation successful.
Debug = true
[tester::#OO8] Running tests for Stage #OO8 (Print a prompt)
[tester::#OO8] Running ./your_program.sh
[your-program] $ 
[tester::#OO8] ✓ Received prompt
[tester::#OO8] Test passed.
[tester::#CZ2] Running tests for Stage #CZ2 (Handle invalid commands)
[tester::#CZ2] Running ./your_program.sh
[your-program] $ i
[tester::#CZ2] Output does not match expected value.
[tester::#CZ2] Expected: "$ invalid_banana_command"
[tester::#CZ2] Received: "$ i"
[tester::#CZ2] Assertion failed.
[tester::#CZ2] Test failed

```

Output from `codecrafters test`

```auto
[compile] Moved ./.codecrafters/run.sh → ./your_program.sh
[compile] Compilation successful.
Debug = true
[tester::#QP2] Running tests for Stage #QP2 (Autocompletion - Builtin completion)
[tester::#QP2] Running ./your_program.sh
[tester::#QP2] ✓ Received prompt ($ )
[tester::#QP2] Typed "ech"
[your-program] $ e
[tester::#QP2] Output does not match expected value.
[tester::#QP2] Expected: "$ ech"
[tester::#QP2] Received: "$ e"
[tester::#QP2] Assertion failed.
[tester::#QP2] Test failed

```

### Local Env

Here’s a GIF of it working fine on my local machine:  
 ![2025-03-11 10.42.39](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/d/de06a9b86afe0dc55df8157725ceaf1cd5e95961.gif)

### Hypothesis

I suspect that setting the terminal to raw mode with:

```auto
term.MakeRaw

```

is causing issues in the test environment. I need raw mode to capture tab keystrokes for autocompletion, but it seems to interfere with CodeCrafters’ testing setup.

If I switch to:

```auto
bufio.NewReader

```

all tests pass, but then I lose the ability to capture `\t` (tab) and other special characters.

Previously, I attempted using the `go-tty` library ([mattn/go-tty](https://github.com/mattn/go-tty)), and ran into the same issue—likely because it also puts the terminal in raw mode. This makes me think the test environment doesn’t handle raw mode properly.

### Relevant code

My code is spread across multiple files, so it’s tricky to share everything, but here’s the most relevant snippet:

```go
// readlineWithCompletion: Grabs keystrokes in raw mode to handle special keys.
func (shell *Shell) readlineWithCompletion() (string, error) {
    fd, ok := isTerminal(shell.readIn)
    tty := int(fd.Fd())
    if !ok {
        return bufio.NewReader(shell.readIn).ReadString('\n')
    }

    oldState, err := term.MakeRaw(tty)
    if err != nil {
        return bufio.NewReader(shell.readIn).ReadString('\n')
    }
    defer term.Restore(tty, oldState)

    var input []rune
    for {
        keyPress, _, err := bufio.NewReader(shell.readIn).ReadRune()
        if err != nil {
            return "", err
        }

        switch key(keyPress) {
        case keyEnter:
            fmt.Fprint(shell.writerOut, "\r\n")
            return string(input), nil
        case keyTab:
            currInput := string(input)
            completed := shell.completionHandler.complete(currInput)
            if completed != currInput {
                input = []rune(completed)
                fmt.Fprintf(shell.writerOut, "\r$ %s", completed)
            }
        case keyBackspace:
            if len(input) > 0 {
                input = input[:len(input)-1]
                fmt.Fprint(shell.writerOut, "\b \b")
            }
        case keyCtrlC:
            fmt.Fprintf(shell.writerOut, "^C\r\n")
            return "", nil
        default:
            input = append(input, keyPress)
            fmt.Fprintf(shell.writerOut, "%c", keyPress)
        }
    }
}

```

```auto
// complete: Simplistic prefix-based completion for built-in commands
func (c *completionHandler) complete(input string) string {
    if len(input) == 0 {
        return input
    }
    fields := strings.Fields(input)
    prefix := fields[len(fields)-1]
    var matches []string

    for _, completion := range c.completions {
        if strings.HasPrefix(completion, prefix) {
            matches = append(matches, completion)
        }
    }
    if len(matches) == 0 {
        return input
    }
    return matches[0]
}

```

Please let me know if you need anything else from me.

Any help on this would be really appreciated!! Thanks in advance!

---

<div class="post-metadata">

**Author:** ![dgiridharan](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/dgiridharan/32/6534_2.png) [@dgiridharan](https://forum.codecrafters.io/u/dgiridharan)\
**Post date:** [March 12, 2025, 5:19am UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/3 "2025-03-12T05:19:39Z")

</div>

Note: This seems to be a related topic:  
[https://forum.codecrafters.io/t/stuck-on-stage-qp2/4294/13](https://forum.codecrafters.io/t/stuck-on-stage-qp2/4294/13)

However, I’m already doing the suggested solution.

---

<div class="post-metadata">

**Author:** ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)\
**Post date:** [March 12, 2025, 8:15am UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/4 "2025-03-12T08:15:57Z")

</div>

Hey @dgiridharan, thanks for the detailed explanation!

The issue seems to be caused by creating a new `bufio.NewReader` for each character read inside the loop:

 ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/6/645526c3be4a51b5e9c7110273f9b0a26c952ae9.png)

This resets the reader on every iteration, causing buffered input to be lost and preventing it from maintaining its state properly.

Try moving the creation of `bufio.NewReader` outside the loop to preserve the buffer. Let me know if that helps!

---

<div class="post-metadata">

**Author:** ![dgiridharan](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/dgiridharan/32/6534_2.png) [@dgiridharan](https://forum.codecrafters.io/u/dgiridharan)\
**Post date:** [March 12, 2025, 2:06pm UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/5 "2025-03-12T14:06:24Z")

</div>

Wow, thanks for the quick response @andy1li!

Move this line outside of the main loop in `shell.Start()` fixed the issue and now I’m passing the tests for this stage!

```auto
func (shell *Shell) Start() error {
	shell.running = true
	reader := bufio.NewReader(shell.readIn)
	for shell.running {
		// Display prompt
		if _, err := fmt.Fprint(shell.writerOut, "$ "); err != nil {
			return err
		}

		// Wait for user input
		input, err := shell.readlineWithCompletion(reader)
		if err != nil {
			return err
		}

		// Skip empty commands
		input = strings.Trim(input, "\n ")
		if input == "" {
			continue
		}

		// Parse the user input and execute the cmd
		p := parser.NewParser(input)
		cmd, err := p.Parse(shell.exeToPaths)
		if err != nil {
			fmt.Fprintf(shell.writerOut, "Error parsing input: %s - error: %s\n", input, err)
			continue
		}

		// Skip empty cmds
		if cmd == nil {
			continue
		}
		shell.execCmd(cmd)
	}

	return nil
}

```

However the previous stage tests still fail:

```auto
❯ codecrafters test --previous
Initiating test run...
⚡ This is a turbo test run. https://codecrafters.io/turbo
Running tests. Logs should appear shortly...
[compile] Moved ./.codecrafters/run.sh → ./your_program.sh
[compile] Compilation successful.
Debug = true
[tester::#OO8] Running tests for Stage #OO8 (Print a prompt)
[tester::#OO8] Running ./your_program.sh
[your-program] $ 
[tester::#OO8] ✓ Received prompt
[tester::#OO8] Test passed.
[tester::#CZ2] Running tests for Stage #CZ2 (Handle invalid commands)
[tester::#CZ2] Running ./your_program.sh
[your-program] $ invalid_mango_command
[your-program]                        
[tester::#CZ2] Output does not match expected value.
[tester::#CZ2] Expected: "invalid_mango_command: command not found"
[tester::#CZ2] Received: " "
[tester::#CZ2] Assertion failed.
[tester::#CZ2] Test failed
View our article on debugging test failures: https://codecrafters.io/debug

```

This is working locally:  
 ![2025-03-12 12.50.32](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/8/86c604059a48a828f246b20b92bcf702d64dbcd7.gif)

Any ideas?

Thank you again 🙂

---

<div class="post-metadata">

**Author:** ![dgiridharan](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/dgiridharan/32/6534_2.png) [@dgiridharan](https://forum.codecrafters.io/u/dgiridharan)\
**Post date:** [March 12, 2025, 11:14pm UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/7 "2025-03-12T23:14:06Z")

</div>

I’m currently looking at the test case repository to figure out how to test this locally and debug it.  
Is this the test case for an invalid command?

> <https://github.com/codecrafters-io/shell-tester/blob/0ac5bbcf732925e5643ad6bd4e8783868f32bd5a/internal/stage2.go>

I assume I should be able to reproduce this by running it locally, but it’s not straightforward.

I tried using `fmt.Printf()` statements, but they don’t seem to appear when I run the test using `codecrafters test --previous`. What am I missing? 🤔

I already have `debug` set to `true` in `codecrafters.yml`

---

<div class="post-metadata">

**Author:** ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)\
**Post date:** [March 13, 2025, 7:17am UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/8 "2025-03-13T07:17:03Z")

</div>

The issue occurs due to differences in how mac and linux handle the “Enter” key.

I added a log here:

 ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/6/68eaebf765cc3420cf10963fa2cd432ec15be630.png)

For mac, it’s `\r` (13):

 ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/0/005b66fb2adde47ad92b0b1f8fe8b734aae05b8e.png)

For linux, it’s `\n` (10):

 ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/2/2a66be9c14dfbfed1baf615eb002847b00ece01c.jpeg)

Once your code handles both \r and \n, the issue should be resolved:

 ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/8/883c083e70d16509e31988b75e20d39c1a689f40.png)

---

<div class="post-metadata">

**Author:** ![dgiridharan](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/dgiridharan/32/6534_2.png) [@dgiridharan](https://forum.codecrafters.io/u/dgiridharan)\
**Post date:** [March 13, 2025, 7:39am UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/9 "2025-03-13T07:39:34Z")

</div>

Amazing, thanks @andy1li! I just finished all of the portions for the shell challenge 🙂

OOC - when I tried to print out using `fmt.Fprintf()` or `fmt.Println()` etc…the logs include my print statements of `codecrafters test --previous`.

I’ve already set the `debug: true` in codecrafters.yml file. Is there anything else that I need to do?

---

<div class="post-metadata">

**Author:** ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)\
**Post date:** [March 13, 2025, 8:12am UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/10 "2025-03-13T08:12:27Z")

</div>

Setting `debug: true` only enables additional tester output. It shouldn’t affect your own print statements.

Let me know which specific print statements in your codebase aren’t working, and I can take a closer look.

---

<div class="post-metadata">

**Author:** ![dgiridharan](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/dgiridharan/32/6534_2.png) [@dgiridharan](https://forum.codecrafters.io/u/dgiridharan)\
**Post date:** [March 13, 2025, 5:51pm UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/11 "2025-03-13T17:51:58Z")

</div>

@andy1li, I just tried a few print statements and the test is correctly displaying:  
`[your-program]` Debug - message:…`

So, maybe I just missed it earlier 🤔 Unclear!

But I really want to thank you with all of the assistance and prompt responses! I really appreciate it 🙂

---

<div class="post-metadata">

**Author:** ![system](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/3X/7/0/700657133935c15703e22c7c8870394f6e6dc27d.svg) [@system](https://forum.codecrafters.io/u/system)\
**Post date:** [March 19, 2025, 3:50am UTC](https://forum.codecrafters.io/t/go-stage-qp2-builtin-command-autocompletion-works-locally-but-fails-in-tests/6520/13 "2025-03-19T03:50:45Z")

</div>

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