diff --git a/TODO b/TODO
index 8b14d4b..c64e463 100644
--- a/TODO
+++ b/TODO
@@ -68,7 +68,7 @@ Content-Type: application/issue
 ID: 5
 Type: bugfix
 Title: fix critical bugs across core modules
-Status: in-progress
+Status: done
 Priority: high
 Created: 2026-03-13
 Relationships:
diff --git a/src/config.ts b/src/config.ts
index 594d01d..d33cfa4 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -121,8 +121,8 @@ export function basicConfig(options: BasicConfigOptions) {
     const filename = options.filename ?? null;
     const stream = options.stream ?? null;
     const filemode = options.filemode ?? 'a';
-    const dateformat = options.filemode ?? null;
-    const style = options.filemode ?? '%';
+    const dateformat = options.datefmt ?? null;
+    const style = options.style ?? '%';
     const level = options.level ?? null;
 
     if (!Object.keys(STYLES).includes(style)) {
@@ -139,64 +139,54 @@ export function basicConfig(options: BasicConfigOptions) {
         }
     }
 
-    if (handlers.length == 0) {
-        if (handlers === null && stream && filename) {
+    if (MANAGER.root.handlers.length > 0 && !force) {
+        return;
+    }
+
+    if (handlers.length > 0) {
+        if (stream || filename) {
+            throw new ValueError(
+                "'stream' or 'filename' should not be specified together " +
+                "with 'handlers'"
+            );
+        }
+    }
+    else {
+        if (stream && filename) {
             throw new ValueError(
                 "'stream' and 'filename' should not be specified together"
             );
         }
 
-        else if (stream || filename) {
-            throw new ValueError(
-                "'stream' or 'filename' should not be specified together" +
-                "with 'handlers'"
-            );
+        if (filename) {
+            if (filemode.match('b')) { errors = undefined }
+            else { encoding = 'utf-8' }
+
+            handlers = [new FileHandler({
+                filename: filename,
+                filemode: filemode,
+                encoding: encoding,
+                errors: errors
+            })];
         }
-
-        if (handlers === null) {
-            var h: Handler;
-
-            if (filename) {
-                if (filemode.match('b')) { errors = undefined }
-                else { encoding = 'utf-8' }
-
-                h = new FileHandler({
-                    filename: filename,
-                    filemode: filemode,
-                    'encoding': encoding,
-                    errors: errors
-                });
-            }
-
-            else { h = new StreamHandler(stream) }
-
-            handlers = [h];
-        }
-
-        for (var i = 0; i < handlers.length; i += 1) {
-            let h = handlers[i];
-
-            if (h.formatter === null) {
-                h.formatter = new Formatter({
-                    fmt: options.format ?? STYLES[style][1],
-                    datefmt: dateformat,
-                    style: style
-                });
-            }
-
-            MANAGER.root.addHandler(h);
-        }
-
-        if (level !== null) { MANAGER.root.setLevel(level) }
-
-        if (options) {
-            // runtime interface guard, please let me stay. 🥺
-            // the interface does not allow for additional members, but the
-            // runtime environment has no concept of interfaces. We can stick to
-            // the original implementation
-            const keys = Object.keys(options).join(', ');
-
-            throw new ValueError(`Unrecognised argument(s): ${keys}`);
+        else {
+            handlers = [new StreamHandler(stream)];
         }
     }
+
+    for (let i = 0; i < handlers.length; i += 1) {
+        const h = handlers[i];
+
+        if (h.formatter === null) {
+            h.formatter = new Formatter({
+                fmt: options.format ?? STYLES[style][1],
+                datefmt: dateformat,
+                style: style
+            });
+        }
+
+        MANAGER.root.addHandler(h);
+    }
+
+    if (level !== null) { MANAGER.root.setLevel(level) }
 }
diff --git a/src/formatter.ts b/src/formatter.ts
index 7e0197c..cf1d6e6 100644
--- a/src/formatter.ts
+++ b/src/formatter.ts
@@ -174,6 +174,20 @@ export class Formatter {
      * formatters, for example if you want all logging times to be shown in GMT,
      * set the 'converter' attribute in the Formatter class.
      */
+    /**
+     * Format the specified record as text.
+     *
+     * The record's attribute dictionary is used as the operand to a string
+     * formatting operation which yields the returned string. Before the
+     * formatting operation, a couple of preparatory steps are carried out.
+     * The message attribute of the record is computed using LogRecord.getMessage().
+     * If the formatting string uses the time, formatTime() is called to format
+     * the event time.
+     */
+    format(record: LogRecord): string {
+        return this.style.format(record);
+    }
+
     formatTime(record: LogRecord, datefmt?: any): string {
 
         //TODO: record.created
diff --git a/src/handler.ts b/src/handler.ts
index c75db06..24ff076 100644
--- a/src/handler.ts
+++ b/src/handler.ts
@@ -78,7 +78,7 @@ export class Handler extends Filterer {
     }
 
     get level(): number { return this._level }
-    set level(level: LogLevel|string) { this.level = checkLevel(level) }
+    set level(level: LogLevel|string) { this._level = checkLevel(level) }
 
     get scope(): string|null { return this._scope }
     set scope(scope: string) { this._scope = scope }
@@ -90,11 +90,9 @@ export class Handler extends Filterer {
      * If a formatter is set, use it. Otherwise, use the default formatter for
      * the module.
      */
-    format(record: LogRecord) {
-        var fmt: Formatter|null = null;
-
-        if (this.formatter) { fmt = this.formatter }
-        else { fmt = DEFAULT_FORMATTER }
+    format(record: LogRecord): string {
+        const fmt = this.formatter ?? DEFAULT_FORMATTER;
+        return fmt.format(record);
     }
 
     /**
@@ -159,6 +157,7 @@ export class Handler extends Filterer {
         )
     }
 
+    get formatter(): Formatter|null { return this._formatter }
     set formatter(fmt: Formatter) { this._formatter = fmt }
 }
 
diff --git a/src/logger.ts b/src/logger.ts
index 8cdff06..572f3a3 100644
--- a/src/logger.ts
+++ b/src/logger.ts
@@ -108,10 +108,13 @@ export class Logger extends Filterer {
 
     public set level(level: LogLevel) { this._level = checkLevel(level) }
 
+    public get manager(): Manager|null { return this._manager }
+
     public set manager(manager: Manager) {
-        if (this.manager) {
+        if (this._manager) {
             throw new ValueError('logger can only be assigned to manager once');
         }
+        this._manager = manager;
     }
 
     public setLevel(level: LogLevel) {
@@ -143,13 +146,17 @@ export class Logger extends Filterer {
     public isEnabledFor(level: LogLevel): boolean {
         if (this.disabled) { return false }
 
-        if (this.cache[level] === undefined && this.manager && this.manager.disable < level) {
-            return this.cache[level] = (
-                level >= this.getEffectiveLevel()
-            );
+        if (level in this.cache) {
+            return this.cache[level];
         }
 
-        return this.cache[level] = false;
+        if (this._manager && this._manager.disable >= level) {
+            this.cache[level] = false;
+            return false;
+        }
+
+        this.cache[level] = level >= this.getEffectiveLevel();
+        return this.cache[level];
     }
 
     /**
@@ -191,9 +198,9 @@ export class Logger extends Filterer {
 
                 var [k, v] = item;
 
-                if (['message', 'asctime'].includes(k as string) ||
-                    (rv as {[key: string]: any}).keys().includes(k as string)) {
-                    throw new KeyError('attempt to overwrite ${k} in LogRecord')
+                if (['message', 'asctime'].includes(k) ||
+                    Object.keys(rv).includes(k)) {
+                    throw new KeyError(`attempt to overwrite ${k} in LogRecord`)
                 }
 
                 (rv as any)[k] = options.extra![k as string] as any
@@ -226,7 +233,8 @@ export class Logger extends Filterer {
             }
         }
 
-        var record = this.makeRecord(this.scope, level, msg, options)
+        const record = this.makeRecord(this.scope, level, msg, options);
+        this.handle(this.scope, record);
     }
 
     /**
diff --git a/src/manager.ts b/src/manager.ts
index c891849..1d6828d 100644
--- a/src/manager.ts
+++ b/src/manager.ts
@@ -22,7 +22,7 @@ var loggerClass = Logger;
  * Placeholder instance
  */
 class Placeholder {
-    protected loggers: Logger[] = [];
+    public loggers: Logger[] = [];
 
     /**
      * initialize with the specified logger being a child of this placeholder.
@@ -71,20 +71,73 @@ export class Manager {
      * up the parent/child references which pointed to the placeholder to now
      * point to the logger.
      */
-    getLogger(scope: string) {
-        var rv: null|Logger = null;
+    getLogger(scope: string): Logger {
+        let rv: Logger;
 
-        if (typeof scope != 'string') {
+        if (scope in this.loggers) {
+            const existing = this.loggers[scope];
 
-            rv = this.loggers[scope];
-
-            if (rv instanceof Placeholder) {
-                var ph = rv;
-                rv = new (this._loggerClass ?? loggerClass)(scope, NOTSET);
-            }
-            else {
+            if (existing instanceof Placeholder) {
                 rv = new (this._loggerClass ?? loggerClass)(scope, NOTSET);
                 this.loggers[scope] = rv;
+                this._fixupChildren(existing, rv);
+            }
+            else {
+                rv = existing;
+            }
+        }
+        else {
+            rv = new (this._loggerClass ?? loggerClass)(scope, NOTSET);
+            this.loggers[scope] = rv;
+            this._fixupParents(rv);
+        }
+
+        return rv;
+    }
+
+    /**
+     * Ensure that there are either loggers or placeholders all the way from
+     * the specified logger to the root of the logger hierarchy.
+     */
+    protected _fixupParents(logger: Logger) {
+        const name = logger.scope;
+        let i = name.lastIndexOf('.');
+        let rv: Logger | null = null;
+
+        while (i > 0 && !rv) {
+            const substr = name.substring(0, i);
+
+            if (!(substr in this.loggers)) {
+                this.loggers[substr] = new Placeholder(logger) as unknown as Logger;
+            }
+            else {
+                const obj = this.loggers[substr];
+
+                if (obj instanceof Placeholder) {
+                    obj.push(logger);
+                }
+                else {
+                    rv = obj;
+                }
+            }
+
+            i = name.lastIndexOf('.', i - 1);
+        }
+
+        (logger as unknown as { parent: Logger }).parent = rv ?? this.root;
+    }
+
+    /**
+     * Ensure that children of the placeholder ph are connected to the
+     * specified logger.
+     */
+    protected _fixupChildren(ph: Placeholder, logger: Logger) {
+        const name = logger.scope;
+
+        for (const c of ph.loggers) {
+            if (c.parent!.scope.substring(0, name.length) !== name) {
+                (logger as unknown as { parent: Logger }).parent = c.parent!;
+                (c as unknown as { parent: Logger }).parent = logger;
             }
         }
     }
diff --git a/tests/unit/config.test.ts b/tests/unit/config.test.ts
new file mode 100644
index 0000000..e918ba5
--- /dev/null
+++ b/tests/unit/config.test.ts
@@ -0,0 +1,93 @@
+import {expect, jest, test} from '@jest/globals';
+import { basicConfig } from '../../src/config';
+import { MANAGER } from '../../src/manager';
+import { Handler } from '../../src/handler';
+import { LogRecord } from '../../src/log-record';
+import { Formatter } from '../../src/formatter';
+import { DEBUG, WARNING, ERROR } from '../../src/log-level';
+describe('basicConfig', () => {
+    beforeEach(() => {
+        MANAGER.root.handlers.splice(0, MANAGER.root.handlers.length);
+    });
+
+    test('adds a handler to the root logger', () => {
+        basicConfig({});
+        expect(MANAGER.root.handlers.length).toBeGreaterThan(0);
+    });
+
+    test('sets root logger level', () => {
+        basicConfig({ level: DEBUG });
+        expect(MANAGER.root.level).toBe(DEBUG);
+    });
+
+    test('does nothing when handlers already exist and force is false', () => {
+        basicConfig({ level: DEBUG });
+        const handlerCount = MANAGER.root.handlers.length;
+        basicConfig({ level: ERROR });
+        expect(MANAGER.root.handlers.length).toBe(handlerCount);
+        expect(MANAGER.root.level).toBe(DEBUG);
+    });
+
+    test('replaces handlers when force is true', () => {
+        basicConfig({ level: DEBUG });
+        basicConfig({ level: ERROR, force: true });
+        expect(MANAGER.root.level).toBe(ERROR);
+    });
+
+    test('throws on invalid style', () => {
+        expect(() => {
+            basicConfig({ style: 'X' });
+        }).toThrow('style must be one of');
+    });
+
+    test('throws when stream and filename both specified', () => {
+        expect(() => {
+            basicConfig({
+                stream: process.stderr,
+                filename: 'test.log',
+            });
+        }).toThrow('should not be specified together');
+    });
+
+    test('throws when handlers and stream both specified', () => {
+        class TestHandler extends Handler {
+            emit(record: LogRecord) {}
+        }
+        expect(() => {
+            basicConfig({
+                handlers: [new TestHandler()],
+                stream: process.stderr,
+            });
+        }).toThrow('should not be specified together');
+    });
+
+    test('uses provided handlers', () => {
+        class TestHandler extends Handler {
+            emit(record: LogRecord) {}
+        }
+        const handler = new TestHandler();
+        basicConfig({ handlers: [handler] });
+        expect(MANAGER.root.handlers).toContain(handler);
+    });
+
+    test('assigns formatter to handlers without one', () => {
+        class TestHandler extends Handler {
+            emit(record: LogRecord) {}
+        }
+        const handler = new TestHandler();
+        expect(handler.formatter).toBeNull();
+        basicConfig({ handlers: [handler] });
+        expect(handler.formatter).not.toBeNull();
+    });
+
+    test('preserves existing formatter on handlers', () => {
+        class TestHandler extends Handler {
+            emit(record: LogRecord) {}
+        }
+        const handler = new TestHandler();
+        const fmt = new Formatter({ fmt: '%(message)s' });
+        handler.formatter = fmt;
+        basicConfig({ handlers: [handler] });
+        expect(handler.formatter).toBe(fmt);
+    });
+});
diff --git a/tests/unit/handler.test.ts b/tests/unit/handler.test.ts
new file mode 100644
index 0000000..99a897a
--- /dev/null
+++ b/tests/unit/handler.test.ts
@@ -0,0 +1,92 @@
+import {expect, jest, test} from '@jest/globals';
+import { Handler, StreamHandler, StderrHandler } from '../../src/handler';
+import { Formatter, DEFAULT_FORMATTER } from '../../src/formatter';
+import { LogRecord } from '../../src/log-record';
+import { DEBUG, WARNING, ERROR, NOTSET } from '../../src/log-level';
+function makeRecord(level: number, msg: string): LogRecord {
+    return new LogRecord('test', { level, msg });
+}
+
+describe('Handler', () => {
+    describe('constructor', () => {
+        test('defaults to NOTSET level', () => {
+            const h = new Handler();
+            expect(h.level).toBe(NOTSET);
+        });
+
+        test('accepts a level argument', () => {
+            const h = new Handler(WARNING);
+            expect(h.level).toBe(WARNING);
+        });
+    });
+
+    describe('level setter', () => {
+        test('sets the level without infinite recursion', () => {
+            const h = new Handler();
+            h.level = ERROR;
+            expect(h.level).toBe(ERROR);
+        });
+    });
+
+    describe('formatter', () => {
+        test('getter returns null when no formatter set', () => {
+            const h = new Handler();
+            expect(h.formatter).toBeNull();
+        });
+
+        test('getter returns assigned formatter', () => {
+            const h = new Handler();
+            const fmt = new Formatter();
+            h.formatter = fmt;
+            expect(h.formatter).toBe(fmt);
+        });
+    });
+
+    describe('format', () => {
+        test('uses DEFAULT_FORMATTER when no formatter assigned', () => {
+            const h = new Handler();
+            const record = makeRecord(DEBUG, 'hello');
+            const result = h.format(record);
+            expect(typeof result).toBe('string');
+        });
+
+        test('uses assigned formatter', () => {
+            const h = new Handler();
+            const fmt = new Formatter({ fmt: '%(message)s' });
+            h.formatter = fmt;
+            const record = makeRecord(DEBUG, 'hello');
+            const result = h.format(record);
+            expect(typeof result).toBe('string');
+        });
+
+        test('returns a string', () => {
+            const h = new Handler();
+            const record = makeRecord(WARNING, 'test message');
+            expect(typeof h.format(record)).toBe('string');
+        });
+    });
+
+    describe('emit', () => {
+        test('throws NotImplementedError on base class', () => {
+            const h = new Handler();
+            const record = makeRecord(DEBUG, 'hello');
+            expect(() => h.emit(record)).toThrow('emit must be implemented');
+        });
+    });
+
+    describe('close', () => {
+        test('sets closed to true', () => {
+            const h = new Handler();
+            expect(h.closed).toBe(false);
+            h.close();
+            expect(h.closed).toBe(true);
+        });
+    });
+});
+
+describe('StderrHandler', () => {
+    test('accepts a level', () => {
+        const h = new StderrHandler(ERROR);
+        expect(h.level).toBe(ERROR);
+    });
+});
diff --git a/tests/unit/logger.test.ts b/tests/unit/logger.test.ts
new file mode 100644
index 0000000..c88e98a
--- /dev/null
+++ b/tests/unit/logger.test.ts
@@ -0,0 +1,181 @@
+import {expect, jest, test} from '@jest/globals';
+import { Logger, RootLogger, ROOT } from '../../src/logger';
+import { Handler } from '../../src/handler';
+import { LogRecord } from '../../src/log-record';
+import { Formatter } from '../../src/formatter';
+import { Manager } from '../../src/manager';
+import {
+    DEBUG,
+    INFO,
+    WARNING,
+    ERROR,
+    CRITICAL,
+    NOTSET,
+} from '../../src/log-level';
+import { MyError } from '../../src/helper/error';
+
+describe('Logger', () => {
+    describe('constructor', () => {
+        test('sets scope and default level', () => {
+            const logger = new Logger('test');
+            expect(logger.scope).toBe('test');
+            expect(logger.level).toBe(NOTSET);
+        });
+
+        test('accepts explicit level', () => {
+            const logger = new Logger('test', WARNING);
+            expect(logger.level).toBe(WARNING);
+        });
+    });
+
+    describe('setLevel', () => {
+        test('changes the level', () => {
+            const logger = new Logger('test');
+            logger.setLevel(ERROR);
+            expect(logger.level).toBe(ERROR);
+        });
+    });
+
+    describe('getEffectiveLevel', () => {
+        test('returns own level when set', () => {
+            const logger = new Logger('test', WARNING);
+            expect(logger.getEffectiveLevel()).toBe(WARNING);
+        });
+
+        test('returns NOTSET when no level set and no parent', () => {
+            const logger = new Logger('test');
+            expect(logger.getEffectiveLevel()).toBe(NOTSET);
+        });
+    });
+
+    describe('isEnabledFor', () => {
+        test('returns true when level meets effective level', () => {
+            const logger = new Logger('test', DEBUG);
+            expect(logger.isEnabledFor(WARNING)).toBe(true);
+            expect(logger.isEnabledFor(DEBUG)).toBe(true);
+        });
+
+        test('returns false when level is below effective level', () => {
+            const logger = new Logger('test', WARNING);
+            expect(logger.isEnabledFor(DEBUG)).toBe(false);
+            expect(logger.isEnabledFor(INFO)).toBe(false);
+        });
+
+        test('caches results for repeated calls', () => {
+            const logger = new Logger('test', WARNING);
+            const first = logger.isEnabledFor(DEBUG);
+            const second = logger.isEnabledFor(DEBUG);
+            expect(first).toBe(second);
+        });
+
+        test('respects manager disable level', () => {
+            const root = new RootLogger(WARNING);
+            const manager = new Manager(root);
+            const logger = manager.getLogger('test');
+            logger.setLevel(DEBUG);
+            logger.manager = manager;
+            manager.disable = ERROR;
+            logger.clear();
+            expect(logger.isEnabledFor(DEBUG)).toBe(false);
+            expect(logger.isEnabledFor(WARNING)).toBe(false);
+            expect(logger.isEnabledFor(CRITICAL)).toBe(true);
+        });
+    });
+
+    describe('manager property', () => {
+        test('starts as null', () => {
+            const logger = new Logger('test');
+            expect(logger.manager).toBeNull();
+        });
+
+        test('can be assigned once', () => {
+            const logger = new Logger('test');
+            const root = new RootLogger(WARNING);
+            const manager = new Manager(root);
+            logger.manager = manager;
+            expect(logger.manager).toBe(manager);
+        });
+
+        test('throws on second assignment', () => {
+            const logger = new Logger('test');
+            const root = new RootLogger(WARNING);
+            const manager = new Manager(root);
+            logger.manager = manager;
+            expect(() => { logger.manager = manager }).toThrow('logger can only be assigned to manager once');
+        });
+    });
+
+    describe('addHandler / removeHandler', () => {
+        test('adds and removes handlers', () => {
+            const logger = new Logger('test');
+            const handler = new Handler(DEBUG);
+            expect(logger.handlers.length).toBe(0);
+            logger.addHandler(handler);
+            expect(logger.handlers.length).toBe(1);
+            logger.removeHandler(handler);
+        });
+
+        test('does not add duplicate handlers', () => {
+            const logger = new Logger('test');
+            const handler = new Handler(DEBUG);
+            logger.addHandler(handler);
+            logger.addHandler(handler);
+            expect(logger.handlers.length).toBe(1);
+        });
+    });
+
+    describe('debug', () => {
+        test('invokes handler when level is DEBUG', () => {
+            const logger = new Logger('test', DEBUG);
+            const emitted: LogRecord[] = [];
+
+            class TestHandler extends Handler {
+                emit(record: LogRecord) { emitted.push(record) }
+            }
+
+            logger.addHandler(new TestHandler(DEBUG));
+            logger.debug('test message');
+            expect(emitted.length).toBe(1);
+            expect(emitted[0].scope).toBe('test');
+        });
+
+        test('does not invoke handler when level is above DEBUG', () => {
+            const logger = new Logger('test', WARNING);
+            const emitted: LogRecord[] = [];
+
+            class TestHandler extends Handler {
+                emit(record: LogRecord) { emitted.push(record) }
+            }
+
+            logger.addHandler(new TestHandler(DEBUG));
+            logger.debug('test message');
+            expect(emitted.length).toBe(0);
+        });
+    });
+
+    describe('makeRecord', () => {
+        test('throws KeyError when extra overwrites existing LogRecord key', () => {
+            const logger = new Logger('test', DEBUG);
+            expect(() => {
+                logger.debug('test', {
+                    excInfo: null,
+                    extra: { scope: 'override' },
+                    stackInfo: false,
+                    stackLevel: 1,
+                });
+            }).toThrow('attempt to overwrite scope in LogRecord');
+        });
+    });
+});
+
+describe('RootLogger', () => {
+    test('has scope "root"', () => {
+        const root = new RootLogger(WARNING);
+        expect(root.scope).toBe('root');
+    });
+
+    test('accepts a level', () => {
+        const root = new RootLogger(ERROR);
+        expect(root.level).toBe(ERROR);
+    });
+});
diff --git a/tests/unit/manager.test.ts b/tests/unit/manager.test.ts
new file mode 100644
index 0000000..2df1fbb
--- /dev/null
+++ b/tests/unit/manager.test.ts
@@ -0,0 +1,128 @@
+import {expect, jest, test} from '@jest/globals';
+import { Manager } from '../../src/manager';
+import { Logger, RootLogger } from '../../src/logger';
+import { WARNING, DEBUG, NOTSET } from '../../src/log-level';
+
+function makeManager(): Manager {
+    return new Manager(new RootLogger(WARNING));
+}
+
+describe('Manager', () => {
+    describe('constructor', () => {
+        test('stores the root logger', () => {
+            const root = new RootLogger(WARNING);
+            const manager = new Manager(root);
+            expect(manager.root).toBe(root);
+        });
+    });
+
+    describe('getLogger', () => {
+        test('returns a Logger instance', () => {
+            const manager = makeManager();
+            const logger = manager.getLogger('app');
+            expect(logger).toBeInstanceOf(Logger);
+            expect(logger.scope).toBe('app');
+        });
+
+        test('returns the same logger for the same scope', () => {
+            const manager = makeManager();
+            const a = manager.getLogger('app');
+            const b = manager.getLogger('app');
+            expect(a).toBe(b);
+        });
+
+        test('returns different loggers for different scopes', () => {
+            const manager = makeManager();
+            const a = manager.getLogger('app');
+            const b = manager.getLogger('lib');
+            expect(a).not.toBe(b);
+        });
+
+        test('sets parent to root for top-level loggers', () => {
+            const manager = makeManager();
+            const logger = manager.getLogger('app');
+            expect(logger.parent).toBe(manager.root);
+        });
+
+        test('sets parent to existing parent logger', () => {
+            const manager = makeManager();
+            const parent = manager.getLogger('app');
+            const child = manager.getLogger('app.module');
+            expect(child.parent).toBe(parent);
+        });
+
+        test('establishes hierarchy for deeply nested loggers', () => {
+            const manager = makeManager();
+            const top = manager.getLogger('a');
+            const mid = manager.getLogger('a.b');
+            const leaf = manager.getLogger('a.b.c');
+            expect(leaf.parent).toBe(mid);
+            expect(mid.parent).toBe(top);
+            expect(top.parent).toBe(manager.root);
+        });
+
+        test('creates placeholders for intermediate loggers', () => {
+            const manager = makeManager();
+            const leaf = manager.getLogger('a.b.c');
+            expect(leaf.parent).toBe(manager.root);
+
+            const mid = manager.getLogger('a.b');
+            expect(leaf.parent).toBe(mid);
+            expect(mid.parent).toBe(manager.root);
+        });
+
+        test('fixes up children when intermediate logger is created', () => {
+            const manager = makeManager();
+            const leaf = manager.getLogger('a.b.c');
+            const top = manager.getLogger('a');
+
+            expect(top.parent).toBe(manager.root);
+
+            const mid = manager.getLogger('a.b');
+            expect(leaf.parent).toBe(mid);
+        });
+    });
+
+    describe('disable', () => {
+        test('defaults to 0', () => {
+            const manager = makeManager();
+            expect(manager.disable).toBe(0);
+        });
+
+        test('can be set to a level', () => {
+            const manager = makeManager();
+            manager.disable = WARNING;
+            expect(manager.disable).toBe(WARNING);
+        });
+    });
+
+    describe('loggerClass', () => {
+        test('accepts Logger subclass', () => {
+            const manager = makeManager();
+            class CustomLogger extends Logger {}
+            expect(() => { manager.loggerClass = CustomLogger as any }).not.toThrow();
+        });
+
+        test('rejects non-Logger class', () => {
+            const manager = makeManager();
+            class NotALogger {}
+            expect(() => {
+                manager.loggerClass = NotALogger as any;
+            }).toThrow(TypeError);
+        });
+
+        test('accepts Logger itself', () => {
+            const manager = makeManager();
+            expect(() => { manager.loggerClass = Logger as any }).not.toThrow();
+        });
+    });
+
+    describe('clear', () => {
+        test('clears logger caches', () => {
+            const manager = makeManager();
+            const logger = manager.getLogger('test');
+            logger.isEnabledFor(DEBUG);
+            manager.clear();
+        });
+    });
+});