test: add tests for tab completions

Signed-off-by: Snehil Shah <snehilshah.989@gmail.com>

lib/node_modules/@stdlib/repl/lib/completer_engine.js

@@ -188,7 +188,7 @@ setNonEnumerableReadOnly( CompleterEngine.prototype, '_completionCallback', func
 			// Move the cursor to the start of completion prefix:
 			self._rli.cursor -= self._completionPrefix.length;
 
-			// Write the auto-completion string
+			// Write the auto-completion string:
 			self._rli.write( autoCompletion );
 
 			// Resume the input stream:
@@ -368,6 +368,7 @@ setNonEnumerableReadOnly( CompleterEngine.prototype, '_navigateCompletions', fun
 			output += repeat( ' ', whitespaces );
 		}
 		if ( i === this._output.index && this.repl._isTTY ) {
+			// Highlight the current navigated index:
 			completion = stripANSI( completion );
 			completion = '\u001b[7m' + completion + '\u001b[27m';
 		}
@@ -440,7 +441,6 @@ setNonEnumerableReadOnly( CompleterEngine.prototype, 'beforeKeypress', function
 			// Move to the previous row or if already on the line, stop navigating and trigger default behaviour...
 			if ( this._output.index === -1 ) {
 				readline.clearScreenDown( this._ostream );
-				this._output.index = -1;
 				this.repl._isNavigatingCompletions = false;
 				this._ttyWrite.call( this._rli, data, key );
 				return;
@@ -452,17 +452,31 @@ setNonEnumerableReadOnly( CompleterEngine.prototype, 'beforeKeypress', function
 			}
 			this._navigateCompletions();
 		} else if ( key.name === 'left' ) {
-			// Move back an index...
+			// If on current line, trigger default behaviour and stop navigating...
+			if ( this._output.index === -1 ) {
+				readline.clearScreenDown( this._ostream );
+				this.repl._isNavigatingCompletions = false;
+				this._ttyWrite.call( this._rli, data, key );
+				return;
+			}
+			// If navigating, move back an index...
 			if ( this._output.index > 0 ) {
 				this._output.index -= 1;
+				this._navigateCompletions();
 			}
-			this._navigateCompletions();
 		} else if ( key.name === 'right' ) {
-			// Move ahead an index...
+			// If on current line, trigger default behaviour and stop navigating...
+			if ( this._output.index === -1 ) {
+				readline.clearScreenDown( this._ostream );
+				this.repl._isNavigatingCompletions = false;
+				this._ttyWrite.call( this._rli, data, key );
+				return;
+			}
+			// If navigating, move ahead an index...
 			if ( this._output.index < this._completionsList.length - 1 ) {
 				this._output.index += 1;
+				this._navigateCompletions();
 			}
-			this._navigateCompletions();
 		} else {
 			// For any other keypress, stop navigating and continue default behaviour...
 			readline.clearScreenDown( this._ostream );