Code review comment: +1 for having the if then the logic is more clear for the reader. A comment above the if will also help for reading the code

Code under review:
public void execute() {
        if (this.helpFlag) {
            String commandUsageInfo = BLauncherCmd.getCommandUsageInfo(TEST_COMMAND);
            this.errStream.println(commandUsageInfo);
            return;
        }

        String[] args = LaunchUtils
                .initConfigurations(this.argList == null ? new String[0] : this.argList.toArray(new String[0]));

        
        if (args.length > 1) {
            CommandUtil.printError(this.errStream,
                    "too many arguments.",
                    "ballerina test [--offline] [--sourceroot <path>] [--experimental] [--skip-lock]\n" +
                           "                      [<module-name> | -a | --all]  [--] [(--key=value)...]",
                    false);

            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        if (!this.buildAll && (this.argList == null || this.argList.size() == 0)) {
            CommandUtil.printError(this.errStream,
                    "'test' command requires a module name or '-a | --all' flag " +
                            "to test all the modules of the project.",
                    "ballerina test <module-name> | -a | --all",
                    false);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        this.sourceRootPath = null != this.sourceRoot ?
                Paths.get(this.sourceRoot).toAbsolutePath() : this.sourceRootPath;
        Path sourcePath = null;
        Path targetPath = this.sourceRootPath.resolve(ProjectDirConstants.TARGET_DIR_NAME);

        if (groupList != null && disableGroupList != null) {
            CommandUtil.printError(this.errStream,
                    "Cannot specify both --groups and --disable-groups flags at the same time",
                    "ballerina test --groups <group1, ...> <module-name> | -a | --all",
                    true);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        if ((listGroups && disableGroupList != null) || (listGroups && groupList != null)) {
            CommandUtil.printError(this.errStream,
                    "Cannot specify both --list-groups and --disable-groups/--groups flags at the same time",
                    "ballerina test --list-groups <module-name> | -a | --all",
                    true);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        
        if (this.buildAll) {
            
            if (!ProjectDirs.isProject(this.sourceRootPath)) {
                Path findRoot = ProjectDirs.findProjectRoot(this.sourceRootPath);
                if (null == findRoot) {
                    CommandUtil.printError(this.errStream,
                            "you are trying to test a Ballerina project but there is no Ballerina.toml file.",
                            null,
                            false);
                    CommandUtil.exitError(this.exitWhenFinish);
                    return;
                }

                this.sourceRootPath = findRoot;
            }
        } else if (this.argList.get(0).endsWith(BLangConstants.BLANG_SRC_FILE_SUFFIX)) {
            
            CommandUtil.printError(this.errStream,
                    "test command is only supported inside a Ballerina project",
                    null,
                    false);
            CommandUtil.exitError(this.exitWhenFinish);
        } else if (Files.exists(
                this.sourceRootPath.resolve(ProjectDirConstants.SOURCE_DIR_NAME).resolve(this.argList.get(0))) &&
                Files.isDirectory(
                        this.sourceRootPath.resolve(ProjectDirConstants.SOURCE_DIR_NAME)
                                .resolve(this.argList.get(0)))) {

            
            if (!RepoUtils.isBallerinaProject(this.sourceRootPath)) {
                CommandUtil.printError(this.errStream,
                        "you are trying to test a module that is not inside a project.",
                        null,
                        false);
                CommandUtil.exitError(this.exitWhenFinish);
                return;
            }

            
            if (Paths.get(argList.get(0)).isAbsolute()) {
                CommandUtil.printError(this.errStream,
                        "you are trying to test a module by giving the absolute path. you only need give " +
                                "the name of the module.",
                        "ballerina test <module-name>",
                        true);
                CommandUtil.exitError(this.exitWhenFinish);
                return;
            }

            String moduleName = argList.get(0);

            
            if (moduleName.endsWith("/")) {
                moduleName = moduleName.substring(0, moduleName.length() - 1);
            }

            sourcePath = Paths.get(moduleName);

            
            if (Files.notExists(this.sourceRootPath.resolve(ProjectDirConstants.SOURCE_DIR_NAME).resolve(sourcePath))) {
                CommandUtil.printError(this.errStream,
                        "'" + sourcePath + "' module does not exist.",
                        "ballerina test <module-name>",
                        true);
                CommandUtil.exitError(this.exitWhenFinish);
                return;
            }

        } else {
            CommandUtil.printError(this.errStream,
                    "invalid Ballerina project",
                    "ballerina test  <module-name> | -a | --all",
                    true);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        this.sourceRootPath = this.sourceRootPath.normalize();
        sourcePath = sourcePath == null ? null : sourcePath.normalize();
        targetPath = targetPath.normalize();

        
        CompilerContext compilerContext = new CompilerContext();
        CompilerOptions options = CompilerOptions.getInstance(compilerContext);
        options.put(PROJECT_DIR, this.sourceRootPath.toString());
        options.put(OFFLINE, Boolean.toString(this.offline));
        options.put(COMPILER_PHASE, CompilerPhase.BIR_GEN.toString());
        options.put(LOCK_ENABLED, Boolean.toString(!this.skipLock));
        options.put(TEST_ENABLED, "true");
        options.put(EXPERIMENTAL_FEATURES_ENABLED, Boolean.toString(this.experimentalFlag));
        
        BuildContext buildContext = new BuildContext(this.sourceRootPath, targetPath, sourcePath, compilerContext);
        buildContext.setOut(outStream);
        buildContext.setErr(errStream);

        boolean isSingleFileBuild = buildContext.getSourceType().equals(SINGLE_BAL_FILE);
        

        if (listGroups) {
            testTask = new ListTestGroupsTask();
        } else {
            testTask = new RunTestsTask(groupList, disableGroupList);
        }

        TaskExecutor taskExecutor = new TaskExecutor.TaskBuilder()
                .addTask(new CleanTargetDirTask(), isSingleFileBuild)   
                .addTask(new CreateTargetDirTask()) 
                .addTask(new CompileTask()) 
                .addTask(new CreateBaloTask(), isSingleFileBuild)   
                .addTask(new CreateBirTask())   
                .addTask(new CopyNativeLibTask(skipCopyLibsFromDist))    
                
                .addTask(new CreateJarTask(this.dumpBIR, this.skipCopyLibsFromDist, this.nativeBinary, this.dumpLLVMIR,
                        this.noOptimizeLLVM))
                .addTask(new CopyModuleJarTask(skipCopyLibsFromDist))
                .addTask(testTask) 
                .build();

        taskExecutor.executeTasks(buildContext);

        if (this.exitWhenFinish) {
            Runtime.getRuntime().exit(0);
        }
    }

Line commented on: if (listGroups) {

Revised code:
public void execute() {
        if (this.helpFlag) {
            String commandUsageInfo = BLauncherCmd.getCommandUsageInfo(TEST_COMMAND);
            this.errStream.println(commandUsageInfo);
            return;
        }

        String[] args = LaunchUtils
                .initConfigurations(this.argList == null ? new String[0] : this.argList.toArray(new String[0]));

        
        if (args.length > 1) {
            CommandUtil.printError(this.errStream,
                    "too many arguments.",
                    "ballerina test [--offline] [--sourceroot <path>] [--experimental] [--skip-lock]\n" +
                           "                      [<module-name> | -a | --all]  [--] [(--key=value)...]",
                    false);

            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        if (!this.buildAll && (this.argList == null || this.argList.size() == 0)) {
            CommandUtil.printError(this.errStream,
                    "'test' command requires a module name or '-a | --all' flag " +
                            "to test all the modules of the project.",
                    "ballerina test <module-name> | -a | --all",
                    false);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        this.sourceRootPath = null != this.sourceRoot ?
                Paths.get(this.sourceRoot).toAbsolutePath() : this.sourceRootPath;
        Path sourcePath = null;
        Path targetPath = this.sourceRootPath.resolve(ProjectDirConstants.TARGET_DIR_NAME);

        if (groupList != null && disableGroupList != null) {
            CommandUtil.printError(this.errStream,
                    "Cannot specify both --groups and --disable-groups flags at the same time",
                    "ballerina test --groups <group1, ...> <module-name> | -a | --all",
                    true);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        if ((listGroups && disableGroupList != null) || (listGroups && groupList != null)) {
            CommandUtil.printError(this.errStream,
                    "Cannot specify both --list-groups and --disable-groups/--groups flags at the same time",
                    "ballerina test --list-groups <module-name> | -a | --all",
                    true);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        
        if (this.buildAll) {
            
            if (!ProjectDirs.isProject(this.sourceRootPath)) {
                Path findRoot = ProjectDirs.findProjectRoot(this.sourceRootPath);
                if (null == findRoot) {
                    CommandUtil.printError(this.errStream,
                            "you are trying to test a Ballerina project but there is no Ballerina.toml file.",
                            null,
                            false);
                    CommandUtil.exitError(this.exitWhenFinish);
                    return;
                }

                this.sourceRootPath = findRoot;
            }
        } else if (this.argList.get(0).endsWith(BLangConstants.BLANG_SRC_FILE_SUFFIX)) {
            
            
            sourcePath = (Paths.get(this.argList.get(0)).isAbsolute()) ?
                    Paths.get(this.argList.get(0)) : sourceRootPath.resolve(this.argList.get(0));
            sourceRootPath = sourcePath.getParent();

            
            
            if (ProjectDirs.findProjectRoot(this.sourceRootPath) != null) {
                CommandUtil.printError(this.errStream,
                        "you are trying to test a single file within a ballerina project." +
                                " To run tests within a project, the module name must be specified.",
                        "ballerina test <module-name>",
                        false);
                Runtime.getRuntime().exit(1);
                return;
            }

            
            if (Files.notExists(sourcePath)) {
                CommandUtil.printError(this.errStream,
                        "'" + sourcePath + "' Ballerina file does not exist",
                        null,
                        false);
                Runtime.getRuntime().exit(1);
                return;
            }

            
            if (!Files.isRegularFile(sourcePath)) {
                CommandUtil.printError(this.errStream,
                        "'" + sourcePath + "' is not a Ballerina file. check if it is a symlink or shortcut.",
                        null,
                        false);
                Runtime.getRuntime().exit(1);
                return;
            }

            
            try {
                targetPath = Files.createTempDirectory("ballerina-test-" + System.nanoTime());
            } catch (IOException e) {
                throw LauncherUtils.createLauncherException("error occured when creating executable.");
            }
        } else if (Files.exists(
                this.sourceRootPath.resolve(ProjectDirConstants.SOURCE_DIR_NAME).resolve(this.argList.get(0))) &&
                Files.isDirectory(
                        this.sourceRootPath.resolve(ProjectDirConstants.SOURCE_DIR_NAME)
                                .resolve(this.argList.get(0)))) {

            
            if (!RepoUtils.isBallerinaProject(this.sourceRootPath)) {
                CommandUtil.printError(this.errStream,
                        "you are trying to test a module that is not inside a project.",
                        null,
                        false);
                CommandUtil.exitError(this.exitWhenFinish);
                return;
            }

            
            if (Paths.get(argList.get(0)).isAbsolute()) {
                CommandUtil.printError(this.errStream,
                        "you are trying to test a module by giving the absolute path. you only need give " +
                                "the name of the module.",
                        "ballerina test <module-name>",
                        true);
                CommandUtil.exitError(this.exitWhenFinish);
                return;
            }

            String moduleName = argList.get(0);

            
            if (moduleName.endsWith("/")) {
                moduleName = moduleName.substring(0, moduleName.length() - 1);
            }

            sourcePath = Paths.get(moduleName);

            
            if (Files.notExists(this.sourceRootPath.resolve(ProjectDirConstants.SOURCE_DIR_NAME).resolve(sourcePath))) {
                CommandUtil.printError(this.errStream,
                        "'" + sourcePath + "' module does not exist.",
                        "ballerina test <module-name>",
                        true);
                CommandUtil.exitError(this.exitWhenFinish);
                return;
            }

        } else {
            CommandUtil.printError(this.errStream,
                    "invalid Ballerina project",
                    "ballerina test  <module-name> | -a | --all",
                    true);
            CommandUtil.exitError(this.exitWhenFinish);
            return;
        }

        
        this.sourceRootPath = this.sourceRootPath.normalize();
        sourcePath = sourcePath == null ? null : sourcePath.normalize();
        targetPath = targetPath.normalize();

        
        CompilerContext compilerContext = new CompilerContext();
        CompilerOptions options = CompilerOptions.getInstance(compilerContext);
        options.put(PROJECT_DIR, this.sourceRootPath.toString());
        options.put(OFFLINE, Boolean.toString(this.offline));
        options.put(COMPILER_PHASE, CompilerPhase.BIR_GEN.toString());
        options.put(LOCK_ENABLED, Boolean.toString(!this.skipLock));
        options.put(TEST_ENABLED, "true");
        options.put(EXPERIMENTAL_FEATURES_ENABLED, Boolean.toString(this.experimentalFlag));
        
        BuildContext buildContext = new BuildContext(this.sourceRootPath, targetPath, sourcePath, compilerContext);
        buildContext.setOut(outStream);
        buildContext.setErr(errStream);

        boolean isSingleFileBuild = buildContext.getSourceType().equals(SINGLE_BAL_FILE);
        

        TaskExecutor taskExecutor = new TaskExecutor.TaskBuilder()
                .addTask(new CleanTargetDirTask(), isSingleFileBuild)   
                .addTask(new CreateTargetDirTask()) 
                .addTask(new CompileTask()) 
                .addTask(new CreateBaloTask(), isSingleFileBuild)   
                .addTask(new CreateBirTask())   
                .addTask(new CopyNativeLibTask(skipCopyLibsFromDist))    
                
                .addTask(new CreateJarTask(this.dumpBIR, this.skipCopyLibsFromDist, this.nativeBinary, this.dumpLLVMIR,
                        this.noOptimizeLLVM))
                .addTask(new CopyModuleJarTask(skipCopyLibsFromDist))
                
                
                .addTask(new ListTestGroupsTask(), !listGroups) 
                .addTask(new RunTestsTask(), listGroups) 
                .build();

        taskExecutor.executeTasks(buildContext);

        if (this.exitWhenFinish) {
            Runtime.getRuntime().exit(0);
        }
    }