Eventable common tests for #{on,{add,remove}Listener}

src/event/Evented.js

@@ -230,17 +230,9 @@ module.exports = Trait( 'Evented' )
      */
     on( ev, listener )
     {
-        if ( !( typeof ev === 'string' && ev ) ) {
-            throw TypeError( "Missing event identifier" );
-        }
-        else if ( !( this._events[ ev ] ) ) {
-            throw ReferenceError( `Cannot hook undefined event \`${ev}'` );
-        }
+        this._argValidate( ev, listener, 'hook' );
 
-        if ( typeof listener !== 'function' ) {
-            throw TypeError( "Event listener must be a function" );
-        }
-        else if ( this.hooksEvent( ev, listener ) )
+        if ( this.hooksEvent( ev, listener ) )
         {
             throw Error(
                 `Listener has already been bound to event \`${ev}'`
@@ -252,6 +244,33 @@ module.exports = Trait( 'Evented' )
     },
 
 
+    /**
+     * Ensures that EV and LISTENER conform to Eventable
+     *
+     * @O{1} constant time
+     *
+     * @param {string}   ev       event id
+     * @param {Function} listener hook function
+     *
+     * @return {undefined}
+     */
+    _argValidate( ev, listener, action )
+    {
+        if ( !( typeof ev === 'string' && ev ) ) {
+            throw TypeError( "Missing event identifier" );
+        }
+        else if ( !( this._events[ ev ] ) ) {
+            throw ReferenceError(
+                `Cannot ${action} undefined event \`${ev}'`
+            );
+        }
+
+        if ( typeof listener !== 'function' ) {
+            throw TypeError( "Event listener must be a function" );
+        }
+    },
+
+
     /**
      * Adds event listener, ensuring that gaps created by removing listeners
      * are filled if available
@@ -356,9 +375,7 @@ module.exports = Trait( 'Evented' )
      */
     removeListener( ev, listener )
     {
-        if ( !( this._events[ ev ] ) ) {
-            throw Error( `Cannot unhook undefined event \`${ev}'` );
-        }
+        this._argValidate( ev, listener, 'unhook' );
 
         this.unhookEvent( ev, listener );
         return this;

test/event/EventableTestConform.js

@@ -79,30 +79,21 @@ module.exports = ctor =>
 
         [ 'on', 'addListener' ].forEach( x =>
             _onTests( meta_ctor, x ) );
+
+        _rmTests( meta_ctor );
     } );
 };
 
 
-function _onTests( ctor, on )
+function _commonTests( ctor, method )
 {
-    /**
-     * Note that by using _fvoid, we are implicitly testing the requirement
-     * that the listener shall not be required to declare any number of
-     * parameters (because we defined no parameters).
-     */
-    describe( `#${on}`, () =>
-    {
     /**
      * We must test both inputs at once since we cannot otherwise say
      * with confidence which parameter is non-conforming.
      */
     it( 'accepts string event id with listener function', () =>
-        {
-            expect( () =>
-            {
-                ctor()[ on ]( _ev, _fvoid );
-            } ).to.not.throw( Error );
-        } );
+        expect( () => ctor()[ method ]( _ev, _fvoid ) )
+            .to.not.throw( Error ) );
 
 
     /**
@@ -120,7 +111,7 @@ function _onTests( ctor, on )
      */
     it( 'does not accept an empty event id', () =>
     {
-            expect( () => ctor()[ on ]( '', _fvoid ) )
+        expect( () => ctor()[ method ]( '', _fvoid ) )
             .to.throw( TypeError );
     } );
 
@@ -134,7 +125,7 @@ function _onTests( ctor, on )
     {
         _nonstr.forEach( badev =>
         {
-                expect( () => ctor()[ on ]( badev, _fvoid ) )
+            expect( () => ctor()[ method ]( badev, _fvoid ) )
                 .to.throw( TypeError );
         } );
     } );
@@ -147,7 +138,7 @@ function _onTests( ctor, on )
     {
         _nonf.forEach( badf =>
         {
-                expect( () => ctor()[ on ]( _ev, badf ) )
+            expect( () => ctor()[ method ]( _ev, badf ) )
                 .to.throw( TypeError );
         } );
     } );
@@ -166,9 +157,28 @@ function _onTests( ctor, on )
     {
         let inst = ctor();
 
-            expect( inst[ on ]( _ev, _fvoid ) )
+        expect( inst[ method ]( _ev, _fvoid ) )
             .to.equal( inst );
     } );
-    } );
+}
+
+
+function _onTests( ctor, on )
+{
+    /**
+     * Note that by using _fvoid, we are implicitly testing the requirement
+     * that the listener shall not be required to declare any number of
+     * parameters (because we defined no parameters).
+     */
+    describe( `#${on}`, () =>
+    {
+        _commonTests( ctor, on );
+    } );
+}
+
+
+function _rmTests( ctor )
+{
+    _commonTests( ctor, 'removeListener' );
 }