test: add test case

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---

Author: headlessNode

lib/node_modules/@stdlib/ndarray/flatten-by/test/test.js

@@ -191,6 +191,31 @@ tape( 'the function throws an error if provided an invalid `order` option', func
 	}
 });
 
+tape( 'the function throws an error if provided a callback argument which is not a function', function test( t ) {
+	var values;
+	var i;
+
+	values = [
+		'5',
+		5,
+		NaN,
+		true,
+		false,
+		null,
+		void 0
+	];
+	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() {
+			flattenBy( zeros( [ 2, 2, 2 ] ), {}, value );
+		};
+	}
+});
+
 tape( 'by default, the function flattens all dimensions of a provided input ndarray in lexicographic order (row-major, contiguous)', function test( t ) {
 	var expected;
 	var xbuf;
@@ -291,6 +316,65 @@ tape( 'the function supports specifying the callback execution context (row-majo
 	}
 });
 
+tape( 'the function supports specifying the callback execution context (row-major, contiguous, options)', function test( t ) {
+	var expected;
+	var xbuf;
+	var opts;
+	var ord;
+	var ctx;
+	var sh;
+	var st;
+	var dt;
+	var o;
+	var x;
+	var y;
+
+	dt = 'float64';
+	ord = 'row-major';
+	sh = [ 2, 2, 2 ];
+	st = shape2strides( sh, ord );
+	o = strides2offset( sh, st );
+
+	/*
+	* [
+	*   [
+	*     [ 1.0, 2.0 ],
+	*     [ 3.0, 4.0 ]
+	*   ],
+	*   [
+	*     [ 5.0, 6.0 ],
+	*     [ 7.0, 8.0 ]
+	*   ]
+	* ]
+	*/
+	xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
+	x = new ndarray( dt, xbuf, sh, st, o, ord );
+	ctx = {
+		'count': 1
+	};
+	opts = {
+		'depth': 2
+	};
+
+	y = flattenBy( x, opts, clbk, ctx );
+	expected = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
+
+	t.notEqual( y, x, 'returns expected value' );
+	t.notEqual( getData( y ), xbuf, 'returns expected value' );
+	t.strictEqual( isSameFloat64Array( getData( y ), expected ), true, 'returns expected value' );
+	t.deepEqual( getShape( y ), [ 8 ], 'returns expected value' );
+	t.strictEqual( getDType( y ), dt, 'returns expected value' );
+	t.strictEqual( getOrder( y ), 'row-major', 'returns expected value' );
+	t.strictEqual( ctx.count, 9, 'returns expected value' );
+
+	t.end();
+
+	function clbk( v ) {
+		this.count += 1; // eslint-disable-line no-invalid-this
+		return v;
+	}
+});
+
 tape( 'by default, the function flattens all dimensions of a provided input ndarray in lexicographic order (row-major, non-contiguous)', function test( t ) {
 	var expected;
 	var xbuf;
@@ -436,6 +520,65 @@ tape( 'the function supports specifying the callback execution context (column-m
 	}
 });
 
+tape( 'the function supports specifying the callback execution context (column-major, contiguous, options)', function test( t ) {
+	var expected;
+	var xbuf;
+	var opts;
+	var ord;
+	var ctx;
+	var sh;
+	var st;
+	var dt;
+	var o;
+	var x;
+	var y;
+
+	dt = 'float64';
+	ord = 'column-major';
+	sh = [ 2, 2, 2 ];
+	st = shape2strides( sh, ord );
+	o = strides2offset( sh, st );
+
+	/*
+	* [
+	*   [
+	*     [ 1.0, 2.0 ],
+	*     [ 3.0, 4.0 ]
+	*   ],
+	*   [
+	*     [ 5.0, 6.0 ],
+	*     [ 7.0, 8.0 ]
+	*   ]
+	* ]
+	*/
+	xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
+	x = new ndarray( dt, xbuf, sh, st, o, ord );
+	ctx = {
+		'count': 1
+	};
+	opts = {
+		'depth': 2
+	};
+
+	y = flattenBy( x, opts, clbk, ctx );
+	expected = new Float64Array( [ 1.0, 5.0, 3.0, 7.0, 2.0, 6.0, 4.0, 8.0 ] );
+
+	t.notEqual( y, x, 'returns expected value' );
+	t.notEqual( getData( y ), xbuf, 'returns expected value' );
+	t.strictEqual( isSameFloat64Array( getData( y ), expected ), true, 'returns expected value' );
+	t.deepEqual( getShape( y ), [ 8 ], 'returns expected value' );
+	t.strictEqual( getDType( y ), dt, 'returns expected value' );
+	t.strictEqual( getOrder( y ), 'row-major', 'returns expected value' );
+	t.strictEqual( ctx.count, 9, 'returns expected value' );
+
+	t.end();
+
+	function clbk( v ) {
+		this.count += 1; // eslint-disable-line no-invalid-this
+		return v;
+	}
+});
+
 tape( 'by default, the function flattens all dimensions of a provided input ndarray in lexicographic order (column-major, non-contiguous)', function test( t ) {
 	var expected;
 	var xbuf;