text: /**
  * @license Apache-2.0
  *
  * Copyright (c) 2019 The Stdlib Authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *    http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
  
  'use strict';
  
  // MODULES //
  
  var tape = require( 'tape' );
  var proxyquire = require( 'proxyquire' );
  var isnan = require( '@stdlib/math-base-assert-is-nan' );
  var randu = require( '@stdlib/random-iter-randu' );
  var array2iterator = require( '@stdlib/array-to-iterator' );
  var iteratorSymbol = require( '@stdlib/symbol-iterator' );
  var iterEmpty = require( '@stdlib/iter-empty' );
  var iterSubtract = require( './../lib' );
  
  
  // TESTS //
  
  tape( 'main export is a function', function test( t ) {
  	t.ok( true, __filename );
  	t.equal( typeof iterSubtract, 'function', 'main export is a function' );
  	t.end();
  });
  
  tape( 'the function throws an error if provided fewer than two arguments', function test( t ) {
  	t.throws( iterSubtract, Error, 'throws an error' );
  	t.throws( foo, Error, 'throws an error' );
  	t.end();
  
  	function foo() {
  		iterSubtract( randu() );
  	}
  });
  
  tape( 'the function throws an error if provided an iterator argument which is not an iterator protocol-compliant object or a number (first argument)', function test( t ) {
  	var values;
  	var i;
  
  	values = [
  		'5',
  		true,
  		false,
  		null,
  		void 0,
  		{},
  		[],
  		function noop() {}
  	];
  
  	for ( i = 0; i < values.length; i++ ) {
  		t.throws( badValue( values[i] ), TypeError, 'throws an error when provided '+values[i] );
  	}
  	t.end();
  
  	function badValue( value ) {
  		return function badValue() {
  			iterSubtract( value, randu() );
  		};
  	}
  });
  
  tape( 'the function throws an error if provided an iterator argument which is not an iterator protocol-compliant object or a number (second argument)', function test( t ) {
  	var values;
  	var i;
  
  	values = [
  		'5',
  		true,
  		false,
  		null,
  		void 0,
  		{},
  		[],
  		function noop() {}
  	];
  
  	for ( i = 0; i < values.length; i++ ) {
  		t.throws( badValue( values[i] ), TypeError, 'throws an error when provided '+values[i] );
  	}
  	t.end();
  
  	function badValue( value ) {
  		return function badValue() {
  			iterSubtract( randu(), value );
  		};
  	}
  });
  
  tape( 'the function throws an error if provided an iterator argument which is not an iterator protocol-compliant object or a number (third argument)', function test( t ) {
  	var values;
  	var i;
  
  	values = [
  		'5',
  		true,
  		false,
  		null,
  		void 0,
  		{},
  		[],
  		function noop() {}
  	];
  
  	for ( i = 0; i < values.length; i++ ) {
  		t.throws( badValue( values[i] ), TypeError, 'throws an error when provided '+values[i] );
  	}
  	t.end();
  
  	function badValue( value ) {
  		return function badValue() {
  			iterSubtract( randu(), randu(), value );
  		};
  	}
  });
  
  tape( 'the function throws an error if provided an iterator argument which is not an iterator protocol-compliant object or a number (fourth argument)', function test( t ) {
  	var values;
  	var i;
  
  	values = [
  		'5',
  		true,
  		false,
  		null,
  		void 0,
  		{},
  		[],
  		function noop() {}
  	];
  
  	for ( i = 0; i < values.length; i++ ) {
  		t.throws( badValue( values[i] ), TypeError, 'throws an error when provided '+values[i] );
  	}
  	t.end();
  
  	function badValue( value ) {
  		return function badValue() {
  			iterSubtract( randu(), randu(), randu(), value );
  		};
  	}
  });
  
  tape( 'the function returns an iterator protocol-compliant object (infinite iterators)', function test( t ) {
  	var it;
  	var v;
  	var i;
  
  	it = iterSubtract( randu(), randu() );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	for ( i = 0; i < 100; i++ ) {
  		v = it.next();
  		t.equal( typeof v.value, 'number', 'returns expected value' );
  		t.equal( v.done, false, 'returns expected value' );
  	}
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object (scalars)', function test( t ) {
  	var it;
  	var v;
  	var i;
  
  	it = iterSubtract( 4.0, 4.0 );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	for ( i = 0; i < 100; i++ ) {
  		v = it.next();
  		t.equal( typeof v.value, 'number', 'returns expected value' );
  		t.equal( v.done, false, 'returns expected value' );
  	}
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (2 finite iterators)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 5.0 ];
  	values2 = [ 3.0, 4.0 ];
  	expected = [
  		{
  			'value': -2.0,
  			'done': false
  		},
  		{
  			'value': 1.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (scalar argument)', function test( t ) {
  	var expected;
  	var values1;
  	var scalar;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 5.0 ];
  	scalar = 3.0;
  	expected = [
  		{
  			'value': -2.0,
  			'done': false
  		},
  		{
  			'value': 2.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), scalar );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (scalar argument)', function test( t ) {
  	var expected;
  	var values1;
  	var scalar;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 7.0 ];
  	scalar = 3.0;
  	expected = [
  		{
  			'value': 2.0,
  			'done': false
  		},
  		{
  			'value': -4.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( scalar, array2iterator( values1 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (2 finite iterators; unequal length)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 5.0 ];
  	values2 = [ 3.0, 4.0, 5.0, 6.0, 7.0 ];
  	expected = [
  		{
  			'value': -2.0,
  			'done': false
  		},
  		{
  			'value': 1.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (2 finite iterators; unequal length)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 5.0, 5.0, 6.0, 7.0 ];
  	values2 = [ 3.0, 4.0 ];
  	expected = [
  		{
  			'value': -2.0,
  			'done': false
  		},
  		{
  			'value': 1.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (3 finite iterators)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var values3;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0 ];
  	values2 = [ 3.0, 4.0 ];
  	values3 = [ 5.0, 9.0 ];
  	expected = [
  		{
  			'value': -7.0,
  			'done': false
  		},
  		{
  			'value': -11.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ), array2iterator( values3 ) ); // eslint-disable-line max-len
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (scalar arguments)', function test( t ) {
  	var expected;
  	var values1;
  	var scalar1;
  	var scalar2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0 ];
  	scalar1 = 4.0;
  	scalar2 = 5.0;
  	expected = [
  		{
  			'value': (1.0-4.0)-5.0,
  			'done': false
  		},
  		{
  			'value': (2.0-4.0)-5.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), scalar1, scalar2 );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (scalar arguments)', function test( t ) {
  	var expected;
  	var values1;
  	var scalar1;
  	var scalar2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0 ];
  	scalar1 = 4.0;
  	scalar2 = 5.0;
  	expected = [
  		{
  			'value': (4.0-1.0)-5.0,
  			'done': false
  		},
  		{
  			'value': (4.0-2.0)-5.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( scalar1, array2iterator( values1 ), scalar2 );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (scalar arguments)', function test( t ) {
  	var expected;
  	var values1;
  	var scalar1;
  	var scalar2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0 ];
  	scalar1 = 4.0;
  	scalar2 = 5.0;
  	expected = [
  		{
  			'value': (4.0-5.0)-1.0,
  			'done': false
  		},
  		{
  			'value': (4.0-5.0)-2.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( scalar1, scalar2, array2iterator( values1 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (3 finite iterators; unequal length)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var values3;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0 ];
  	values2 = [ 3.0, 4.0, 7.0 ];
  	values3 = [ 5.0, 6.0, 8.0, 9.0, 10.0 ];
  	expected = [
  		{
  			'value': -7.0,
  			'done': false
  		},
  		{
  			'value': -8.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ), array2iterator( values3 ) ); // eslint-disable-line max-len
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (3 finite iterators; unequal length)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var values3;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0, 7.0 ];
  	values2 = [ 3.0, 4.0 ];
  	values3 = [ 5.0, 6.0, 8.0, 9.0, 10.0 ];
  	expected = [
  		{
  			'value': -7.0,
  			'done': false
  		},
  		{
  			'value': -8.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ), array2iterator( values3 ) ); // eslint-disable-line max-len
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (3 finite iterators; unequal length)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var values3;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0, 7.0 ];
  	values2 = [ 3.0, 4.0, 8.0, 9.0 ];
  	values3 = [ 5.0, 6.0 ];
  	expected = [
  		{
  			'value': -7.0,
  			'done': false
  		},
  		{
  			'value': -8.0,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ), array2iterator( values3 ) ); // eslint-disable-line max-len
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	for ( i = 0; i < expected.length; i++ ) {
  		actual.push( it.next() );
  	}
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (3 finite iterators; 1 empty iterator)', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var values3;
  	var actual;
  	var it;
  
  	values1 = [ 1.0, 2.0 ];
  	values2 = [];
  	values3 = [ 5.0, 6.0 ];
  	expected = [
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ), array2iterator( values3 ) ); // eslint-disable-line max-len
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	actual.push( it.next() );
  
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which performs element-wise subtraction (empty iterators)', function test( t ) {
  	var expected;
  	var actual;
  	var it;
  
  	expected = [
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( iterEmpty(), iterEmpty(), iterEmpty(), iterEmpty() );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	actual = [];
  	actual.push( it.next() );
  
  	t.deepEqual( actual, expected, 'returns expected values' );
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which returns `NaN` if an iterated value is non-numeric', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ '1.0', NaN ];
  	values2 = [ 3.0, 4.0 ];
  	expected = [
  		{
  			'value': NaN,
  			'done': false
  		},
  		{
  			'value': NaN,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	for ( i = 0; i < expected.length; i++ ) {
  		actual = it.next();
  		if ( isnan( expected[ i ].value ) ) {
  			t.equal( isnan( actual.value ), true, 'returns expected value' );
  		} else {
  			t.equal( actual.value, expected[ i ].value, 'returns expected value' );
  		}
  		t.equal( actual.done, expected[ i ].done, 'returns expected value' );
  	}
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which returns `NaN` if an iterated value is non-numeric', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ 1.0, 2.0 ];
  	values2 = [ NaN, '4.0' ];
  	expected = [
  		{
  			'value': NaN,
  			'done': false
  		},
  		{
  			'value': NaN,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	for ( i = 0; i < expected.length; i++ ) {
  		actual = it.next();
  		if ( isnan( expected[ i ].value ) ) {
  			t.equal( isnan( actual.value ), true, 'returns expected value' );
  		} else {
  			t.equal( actual.value, expected[ i ].value, 'returns expected value' );
  		}
  		t.equal( actual.done, expected[ i ].done, 'returns expected value' );
  	}
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which returns `NaN` if an iterated value is non-numeric', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ '1.0' ];
  	values2 = [ 3.0 ];
  	expected = [
  		{
  			'value': NaN,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	for ( i = 0; i < expected.length; i++ ) {
  		actual = it.next();
  		if ( isnan( expected[ i ].value ) ) {
  			t.equal( isnan( actual.value ), true, 'returns expected value' );
  		} else {
  			t.equal( actual.value, expected[ i ].value, 'returns expected value' );
  		}
  		t.equal( actual.done, expected[ i ].done, 'returns expected value' );
  	}
  	t.end();
  });
  
  tape( 'the function returns an iterator protocol-compliant object which returns `NaN` if an iterated value is non-numeric', function test( t ) {
  	var expected;
  	var values1;
  	var values2;
  	var actual;
  	var it;
  	var i;
  
  	values1 = [ NaN ];
  	values2 = [ 1.0 ];
  	expected = [
  		{
  			'value': NaN,
  			'done': false
  		},
  		{
  			'done': true
  		}
  	];
  
  	it = iterSubtract( array2iterator( values1 ), array2iterator( values2 ) );
  	t.equal( it.next.length, 0, 'has zero arity' );
  
  	for ( i = 0; i < expected.length; i++ ) {
  		actual = it.next();
  		if ( isnan( expected[ i ].value ) ) {
  			t.equal( isnan( actual.value ), true, 'returns expected value' );
  		} else {
  			t.equal( actual.value, expected[ i ].value, 'returns expected value' );
  		}
  		t.equal( actual.done, expected[ i ].done, 'returns expected value' );
  	}
  	t.end();
  });
  
  tape( 'the returned iterator has a `return` method for closing an iterator (no argument)', function test( t ) {
  	var it;
  	var r;
  
  	it = iterSubtract( randu(), randu() );
  
  	r = it.next();
  	t.equal( typeof r.value, 'number', 'returns a number' );
  	t.equal( r.done, false, 'returns expected value' );
  
  	r = it.next();
  	t.equal( typeof r.value, 'number', 'returns a number' );
  	t.equal( r.done, false, 'returns expected value' );
  
  	r = it.return();
  	t.equal( r.value, void 0, 'returns expected value' );
  	t.equal( r.done, true, 'returns expected value' );
  
  	r = it.next();
  	t.equal( r.value, void 0, 'returns expected value' );
  	t.equal( r.done, true, 'returns expected value' );
  
  	t.end();
  });
  
  tape( 'the returned iterator has a `return` method for closing an iterator (argument)', function test( t ) {
  	var it;
  	var r;
  
  	it = iterSubtract( randu(), randu() );
  
  	r = it.next();
  	t.equal( typeof r.value, 'number', 'returns a number' );
  	t.equal( r.done, false, 'returns expected value' );
  
  	r = it.next();
  	t.equal( typeof r.value, 'number', 'returns a number' );
  	t.equal( r.done, false, 'returns expected value' );
  
  	r = it.return( 'finished' );
  	t.equal( r.value, 'finished', 'returns expected value' );
  	t.equal( r.done, true, 'returns expected value' );
  
  	r = it.next();
  	t.equal( r.value, void 0, 'returns expected value' );
  	t.equal( r.done, true, 'returns expected value' );
  
  	t.end();
  });
  
  tape( 'if an environment supports `Symbol.iterator` and the provided iterators are iterable, the returned iterator is iterable', function test( t ) {
  	var iterSubtract;
  	var rand1;
  	var rand2;
  	var opts;
  	var it1;
  	var it2;
  	var i;
  
  	iterSubtract = proxyquire( './../lib/main.js', {
  		'@stdlib/symbol-iterator': '__ITERATOR_SYMBOL__'
  	});
  
  	opts = {
  		'seed': 12345
  	};
  
  	rand1 = randu( opts );
  	rand1[ '__ITERATOR_SYMBOL__' ] = factory;
  
  	rand2 = randu( opts );
  	rand2[ '__ITERATOR_SYMBOL__' ] = factory;
  
  	it1 = iterSubtract( rand1, rand2 );
  	t.equal( typeof it1[ '__ITERATOR_SYMBOL__' ], 'function', 'has method' );
  	t.equal( it1[ '__ITERATOR_SYMBOL__' ].length, 0, 'has zero arity' );
  
  	it2 = it1[ '__ITERATOR_SYMBOL__' ]();
  	t.equal( typeof it2, 'object', 'returns an object' );
  	t.equal( typeof it2.next, 'function', 'has method' );
  	t.equal( typeof it2.return, 'function', 'has method' );
  
  	for ( i = 0; i < 100; i++ ) {
  		t.equal( it2.next().value, it1.next().value, 'returns expected value' );
  	}
  	t.end();
  
  	function factory() {
  		return randu( opts );
  	}
  });
  
  tape( 'if an environment supports `Symbol.iterator` and the provided iterators are iterable, the returned iterator is iterable (scalars)', function test( t ) {
  	var iterSubtract;
  	var it1;
  	var it2;
  	var i;
  
  	iterSubtract = proxyquire( './../lib/main.js', {
  		'@stdlib/symbol-iterator': '__ITERATOR_SYMBOL__'
  	});
  
  	it1 = iterSubtract( 4.0, 3.0 );
  	t.equal( typeof it1[ '__ITERATOR_SYMBOL__' ], 'function', 'has method' );
  	t.equal( it1[ '__ITERATOR_SYMBOL__' ].length, 0, 'has zero arity' );
  
  	it2 = it1[ '__ITERATOR_SYMBOL__' ]();
  	t.equal( typeof it2, 'object', 'returns an object' );
  	t.equal( typeof it2.next, 'function', 'has method' );
  	t.equal( typeof it2.return, 'function', 'has method' );
  
  	for ( i = 0; i < 100; i++ ) {
  		t.equal( it2.next().value, it1.next().value, 'returns expected value' );
  	}
  	t.end();
  });
  
  tape( 'if an environment does not support `Symbol.iterator`, the returned iterator is not "iterable"', function test( t ) {
  	var iterSubtract;
  	var it;
  
  	iterSubtract = proxyquire( './../lib/main.js', {
  		'@stdlib/symbol-iterator': false
  	});
  
  	it = iterSubtract( randu(), randu() );
  	t.equal( it[ iteratorSymbol ], void 0, 'does not have property' );
  
  	t.end();
  });
  
  tape( 'if a provided iterator is not iterable, the returned iterator is not iterable', function test( t ) {
  	var iterSubtract;
  	var rand;
  	var it;
  
  	iterSubtract = proxyquire( './../lib/main.js', {
  		'@stdlib/symbol-iterator': '__ITERATOR_SYMBOL__'
  	});
  
  	rand = randu();
  	rand[ '__ITERATOR_SYMBOL__' ] = null;
  
  	it = iterSubtract( rand, rand );
  	t.equal( it[ iteratorSymbol ], void 0, 'does not have property' );
  
  	t.end();
  });
  