diff --git a/src/utils/fn.utils.ts b/src/utils/fn.utils.ts
index d6ad8d56..f8d2f7bb 100644
--- a/src/utils/fn.utils.ts
+++ b/src/utils/fn.utils.ts
@@ -11,7 +11,7 @@ export function isEmpty(value: any[] | string): boolean {
 }
 
 export function trim(value: string): string {
-  return typeof value === 'string' ? value.trim() : '';
+  return isNil(value) ? '' : value.trim();
 }
 
 export function has(value: any, prop: string): boolean {
@@ -22,7 +22,7 @@ export function isFunction(value: any) {
   return typeof value === 'function';
 }
 
-export function get(value: any, path: string = '', defaultValue?: any) {
+export function get(value: any, path: string, defaultValue?: any) {
   let result = value;
 
   for (const prop of path.split('.')) {
@@ -64,7 +64,7 @@ export function once(fn: Once): Once {
 }
 
 export function defaultsDeep(target: any, ... sources: any[]): any {
-  return [target].concat(sources || []).reduce((result: any, source: any) => {
+  return [target].concat(sources).reduce((result: any, source: any) => {
     if (!source) {
       return result;
     }
@@ -90,11 +90,8 @@ export function includes(target: string | any[], value: any): boolean {
     return false;
   }
 
-  if (typeof target === 'string') {
-    return target.indexOf(value as string) > -1;
-  }
-
-  return target.indexOf(value) > -1;
+  const index = typeof target === 'string' ? target.indexOf(value as string) : target.indexOf(value);
+  return index > -1;
 }
 
 export function isNil(value: any): boolean {
diff --git a/test/utils/fn.utils.spec.ts b/test/utils/fn.utils.spec.ts
new file mode 100644
index 00000000..fd75a473
--- /dev/null
+++ b/test/utils/fn.utils.spec.ts
@@ -0,0 +1,53 @@
+import * as fn from '../../src/utils/fn.utils';
+
+describe('fn.utils - multipurpose functions', () => {
+  describe('trim', () => {
+    it('returns empty string when input value is null or undefined', () => {
+      expect(fn.trim(null)).toEqual('');
+      expect(fn.trim(undefined)).toEqual('');
+    });
+
+    it('uses native trim method under the hood', () => {
+      const stringSpy = jasmine.createSpyObj('string', ['trim']);
+      stringSpy.trim.and.returnValue('Boo!');
+      expect(fn.trim(stringSpy as string)).toEqual('Boo!');
+    });
+  });
+
+  describe('once', () => {
+    it('executes function only ones', () => {
+      const onceTargetSpy = jasmine.createSpy('once');
+      const onceExecutableFn = fn.once(onceTargetSpy);
+
+      onceExecutableFn('Hello', ', ', 'World');
+      onceExecutableFn('Hello');
+
+      expect(onceTargetSpy).toHaveBeenCalledTimes(1);
+      expect(onceTargetSpy).toHaveBeenCalledWith('Hello', ', ', 'World');
+      expect(onceTargetSpy).not.toHaveBeenCalledWith('Hello');
+    });
+  });
+
+  describe('defaultsDeep', () => {
+    it('uses empty array if there were no sources given', () => {
+      const options = fn.defaultsDeep({ msg: 'Boo!' });
+
+      expect(options).toEqual({ msg: 'Boo!' });
+    });
+  });
+
+  describe('defaultsDeep', () => {
+    it('uses empty array if there were no sources given', () => {
+      const options = fn.defaultsDeep({ msg: 'Boo!' });
+
+      expect(options).toEqual({ msg: 'Boo!' });
+    });
+  });
+
+  describe('includes', () => {
+    it('works with strings', () => {
+      expect(fn.includes('world', 'rl')).toEqual(true);
+      expect(fn.includes('world', 'rrl')).toEqual(false);
+    });
+  });
+});