Runtime Environment Control

public class RuntimeEnvironment {
    /**
     * Get reference to the Application under test.
     * May be created at setup time or lazily at call time based on LazyApplication setting.
     * Must be called on main/test thread if lazy loading is enabled.
     * 
     * Alternative: androidx.test.core.app.ApplicationProvider.getApplicationContext()
     * for cross-platform tests that work on JVM and real devices.
     */
    public static Application getApplication();
    
    /** Internal use only - sets Application supplier for lazy loading */
    public static void setApplicationSupplier(Supplier<Application> applicationSupplier);
    
    /** Returns the configured Application class */
    public static Class<? extends Application> getConfiguredApplicationClass();
    
    /** Sets the Application class to be used */
    public static void setConfiguredApplicationClass(Class<? extends Application> clazz);
}

public class RuntimeEnvironment {
    /** 
     * @deprecated Use getApplication() instead
     * Incompatible with LazyApplication and may be removed
     */
    @Deprecated 
    public static Context systemContext;
    
    /** 
     * @deprecated Use getApplication() instead
     * Accessing directly is incompatible with LazyApplication
     */
    @Deprecated 
    public static volatile Application application;
}

// Get application instance
Application app = RuntimeEnvironment.getApplication();
assertThat(app).isNotNull();

// Check application type
if (RuntimeEnvironment.getConfiguredApplicationClass() == MyCustomApplication.class) {
    MyCustomApplication customApp = (MyCustomApplication) app;
    customApp.doCustomSetup();
}

public class RuntimeEnvironment {
    /**
     * Returns qualifier string describing current Configuration of system resources.
     * Format follows Android resource qualifier rules:
     * https://developer.android.com/guide/topics/resources/providing-resources.html#QualifierRules
     */
    public static String getQualifiers();
    
    /**
     * Returns qualifier string for given configuration and display metrics.
     */
    public static String getQualifiers(Configuration configuration, DisplayMetrics displayMetrics);
    
    /**
     * Overrides current device configuration.
     * If qualifiers start with '+', overlays on prior configuration additively.
     * Otherwise uses default values for unspecified properties.
     * 
     * See: http://robolectric.org/device-configuration/
     */
    public static void setQualifiers(String newQualifiers);
    
    /** Sets font scale for the device */
    public static void setFontScale(float fontScale);
    
    /** Returns current font scale */
    public static float getFontScale();
}

// Check current configuration
String qualifiers = RuntimeEnvironment.getQualifiers();
assertThat(qualifiers).contains("mdpi");

// Change to tablet landscape configuration
RuntimeEnvironment.setQualifiers("xlarge-land-mdpi");

// Overlay additional qualifiers (additive)
RuntimeEnvironment.setQualifiers("+fr-rFR");  // Add French locale

// Test font scaling
RuntimeEnvironment.setFontScale(1.5f);
assertThat(RuntimeEnvironment.getFontScale()).isEqualTo(1.5f);

// Verify resources update
Resources resources = RuntimeEnvironment.getApplication().getResources();
Configuration config = resources.getConfiguration();
assertThat(config.fontScale).isEqualTo(1.5f);

public class RuntimeEnvironment {
    /**
     * @deprecated Not supported in realistic looper mode
     * Tests if given thread is currently set as main thread.
     */
    @Deprecated
    public static boolean isMainThread(Thread thread);
    
    /**
     * @deprecated Not supported in realistic looper mode  
     * Tests if current thread is main thread.
     */
    @Deprecated
    public static boolean isMainThread();
    
    /**
     * @deprecated Not supported in realistic looper mode
     * Retrieves main thread. Defaults to thread that initializes RuntimeEnvironment.
     */
    @Deprecated
    public static Thread getMainThread();
    
    /**
     * @deprecated Not supported in realistic looper mode
     * Sets the main thread.
     */
    @Deprecated
    public static void setMainThread(Thread newMainThread);
}

public class RuntimeEnvironment {
    /** Returns the activity thread object */
    public static Object getActivityThread();
    
    /** Sets the activity thread object */
    public static void setActivityThread(Object newActivityThread);
}

// Access activity thread for advanced operations
Object activityThread = RuntimeEnvironment.getActivityThread();
// Cast and use as needed for specific test scenarios

public class RuntimeEnvironment {
    /** Returns the Android API level being simulated */
    public static int getApiLevel();
}

// Check API level for conditional test logic
int apiLevel = RuntimeEnvironment.getApiLevel();
if (apiLevel >= Build.VERSION_CODES.Q) {
    // Test API 29+ specific functionality
}

// Assert expected API level
assertThat(RuntimeEnvironment.getApiLevel()).isEqualTo(28);

public class RuntimeEnvironment {
    /**
     * @deprecated Use PAUSED Looper mode instead
     * Retrieves current master scheduler used by main Looper and optionally all Loopers.
     */
    @Deprecated
    public static Scheduler getMasterScheduler();
    
    /**
     * @deprecated Use PAUSED Looper mode instead  
     * Sets current master scheduler. Primarily for Robolectric core setup.
     * Changing during test will have unpredictable results.
     */
    @Deprecated
    public static void setMasterScheduler(Scheduler masterScheduler);
}

public class RuntimeEnvironment {
    /** Sets the temporary directory for test operations */
    public static void setTempDirectory(TempDirectory tempDirectory);
    
    /** Returns the current temporary directory */
    public static TempDirectory getTempDirectory();
}

// Get temp directory for test files
TempDirectory tempDir = RuntimeEnvironment.getTempDirectory();
File testFile = tempDir.create("test-data.txt");

// Write test data
Files.write(testFile.toPath(), "test data".getBytes());

public class RuntimeEnvironment {
    /** Sets the path to Android framework JAR */
    public static void setAndroidFrameworkJarPath(Path localArtifactPath);
    
    /** Returns the path to Android framework JAR */
    public static Path getAndroidFrameworkJarPath();
}

public class RuntimeEnvironment {
    /** Internal use only - sets compile-time system resources supplier */
    public static void setCompileTimeSystemResources(Supplier<Path> compileTimeSystemResourcesSupplier);
    
    /** @deprecated Obsolete, do not use */
    @Deprecated
    public static Path getCompileTimeSystemResourcesPath();
}

// Phone configurations
RuntimeEnvironment.setQualifiers("normal-mdpi");      // Standard phone
RuntimeEnvironment.setQualifiers("normal-hdpi");      // High-DPI phone
RuntimeEnvironment.setQualifiers("normal-xhdpi");     // Extra high-DPI phone
RuntimeEnvironment.setQualifiers("normal-xxhdpi");    // XX high-DPI phone

// Tablet configurations  
RuntimeEnvironment.setQualifiers("large-mdpi");       // 7" tablet
RuntimeEnvironment.setQualifiers("xlarge-mdpi");      // 10" tablet

// Portrait (default)
RuntimeEnvironment.setQualifiers("normal-port-mdpi");

// Landscape
RuntimeEnvironment.setQualifiers("normal-land-mdpi");

// English (default)
RuntimeEnvironment.setQualifiers("en-rUS");

// Other languages
RuntimeEnvironment.setQualifiers("fr-rFR");   // French
RuntimeEnvironment.setQualifiers("es-rES");   // Spanish
RuntimeEnvironment.setQualifiers("ja-rJP");   // Japanese

// Add language to existing configuration
RuntimeEnvironment.setQualifiers("+es-rES");

// Light mode (default)
RuntimeEnvironment.setQualifiers("notnight");

// Dark mode
RuntimeEnvironment.setQualifiers("night");

// Add to existing configuration
RuntimeEnvironment.setQualifiers("+night");

// Large tablet in landscape with high DPI and French locale
RuntimeEnvironment.setQualifiers("fr-rFR-xlarge-land-xhdpi");

// Phone in dark mode with extra large font
RuntimeEnvironment.setQualifiers("normal-port-night-mdpi");
RuntimeEnvironment.setFontScale(1.3f);