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Testing APC Sequence Processing in Termux-App Terminal Emulator

A test suite validating Application Program Command (APC) handling in the Termux terminal emulator, focusing on graphics protocol support and non-printable character processing.

Test Coverage Overview

The test suite provides comprehensive coverage of APC sequence handling in terminal operations.

Key areas tested include:

Kitty graphics protocol support probing
APC sequence consumption behavior
Non-printable character handling within APC strings
Terminal display integrity after APC processing

Implementation Analysis

The testing approach employs JUnit framework features for terminal emulation verification. The implementation uses a fluent interface pattern with chained assertions to validate terminal state and output.

Technical patterns include:

Terminal size configuration testing
Escape sequence processing validation
String display verification
State maintenance checking

Technical Details

Testing infrastructure includes:

JUnit test framework
TerminalTestCase base class for emulation testing
Custom assertion methods for terminal state verification
Terminal size manipulation utilities
Escape sequence handling verification tools

Best Practices Demonstrated

The test suite exemplifies high-quality testing practices through isolated test cases and comprehensive state verification.

Notable practices include:

Clear test case documentation with reference links
Explicit test scenarios for edge cases
Comprehensive output validation
Real-world use case testing

termux/termux-app

terminal-emulator/src/test/java/com/termux/terminal/ApcTest.java

            
package com.termux.terminal;

public class ApcTest extends TerminalTestCase {

    public void testApcConsumed() {
        // At time of writing this is part of what yazi sends for probing for kitty graphics protocol support:
        // https://github.com/sxyazi/yazi/blob/0cdaff98d0b3723caff63eebf1974e7907a43a2c/yazi-adapter/src/emulator.rs#L129
        // This should not result in anything being written to the screen: If kitty graphics protocol support
        // is implemented it should instead result in an error code on stdin, and if not it should be consumed
        // silently just as xterm does. See https://sw.kovidgoyal.net/kitty/graphics-protocol/.
        withTerminalSized(2, 2)
            .enterString("\033_Gi=31,s=1,v=1,a=q,t=d,f=24;AAAA\033\\")
            .assertLinesAre("  ", "  ");

        // It is ok for the APC content to be non printable characters:
        withTerminalSized(12, 2)
            .enterString("hello \033_some\023\033_\\apc#end\033\\ world")
            .assertLinesAre("hello  world", "            ");
    }

}