Task: #53687 Handle missing mode fallback and add no-mode cfg tests

tests/CfgTest.php

@@ -44,6 +44,25 @@ class CfgTest extends TestCase
 		$this->assertSame('218523', $cfg['auth']['projectId']);
 	}
 
+	public function testWriteWithoutModeFallsBackToDefaultMode(): void
+	{
+		file_put_contents(
+			$this->tmpDir.'/config/myCEESV.default.conf.php',
+			"<?php return [\n\t'auth' => [\n\t\t'projectId' => '',\n\t],\n];\n"
+		);
+
+		$result = $this->runCfg([
+			'-a',
+			$this->tmpDir,
+			'write',
+			'myCEESV',
+			'auth:projectId="218523"',
+		]);
+
+		$this->assertSame(0, $result['code'], $result['output']);
+		$this->assertFileExists($this->tmpDir.'/config/myCEESV.conf.php');
+	}
+
 	public function testWriteWithDirectoryNameCreatesAndWritesSiteConfig(): void
 	{
 		$result = $this->runCfg([

tests/SettingsTest.php

@@ -192,6 +192,15 @@ class SettingsTest extends TestCase
 		$cfg = $this->appPath($cfg, 'localOverride')->load();
 		$this->assertEquals(42, $cfg->answer);
 	}
+
+	public function testLoadWithoutModeFallsBackToFirstKnownMode(): void
+	{
+		$cfg = new Settings();
+		$cfg = $this->appPath($cfg, 'noMode')->load();
+
+		$this->assertEquals('prod', $cfg->mode);
+		$this->assertEquals('default', $cfg->testFiles);
+	}
 	
 	/**
 	 * @dataProvider fileNameData

tests/cfg/noMode/config/default.conf.php

@@ -0,0 +1,3 @@
+<?php return [
+	'testFiles' => 'default',
+];