test: ensure no errors when gamma is not available

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---

Author: Planeshifter

lib/node_modules/@stdlib/math/base/special/gamma/test/other/xtest.gamma.js

@@ -21,7 +21,7 @@
 // MODULES //
 
 var tape = require( 'tape' );
-var gamma = require( 'gamma' ); // eslint-disable-line stdlib/require-file-extensions
+var tryRequire = require( '@stdlib/utils/try-require' );
 var isnan = require( '@stdlib/math/base/assert/is-nan' );
 var incrspace = require( '@stdlib/array/base/incrspace' );
 var abs = require( '@stdlib/math/base/special/abs' );
@@ -30,6 +30,14 @@ var PINF = require( '@stdlib/constants/float64/pinf' );
 var NINF = require( '@stdlib/constants/float64/ninf' );
 
 
+// VARIABLES //
+
+var gamma = tryRequire( 'gamma' );
+var opts = {
+	'skip': ( gamma instanceof Error )
+};
+
+
 // FIXTURES //
 
 var data1 = require( './../fixtures/r/data1.json' );
@@ -40,13 +48,13 @@ var expected2 = require( './../fixtures/r/expected2.json' );
 
 // TESTS //
 
-tape( 'main export is a function', function test( t ) {
+tape( 'main export is a function', opts, function test( t ) {
 	t.ok( true, __filename );
 	t.strictEqual( typeof gamma, 'function', 'main export is a function' );
 	t.end();
 });
 
-tape( 'if provided a negative integer, the function returns `NaN`', function test( t ) {
+tape( 'if provided a negative integer, the function returns `NaN`', opts, function test( t ) {
 	var values = incrspace( -1.0, -1000.0, -1.0 );
 	var v;
 	var i;
@@ -58,31 +66,31 @@ tape( 'if provided a negative integer, the function returns `NaN`', function tes
 	t.end();
 });
 
-tape( 'if provided negative infinity, the function returns `NaN`', function test( t ) {
+tape( 'if provided negative infinity, the function returns `NaN`', opts, function test( t ) {
 	var v = gamma( NINF );
 	t.strictEqual( isnan( v ), true, 'returns NaN when provided negative infinity' );
 	t.end();
 });
 
-tape( 'if provided `NaN`, the function returns `NaN`', function test( t ) {
+tape( 'if provided `NaN`, the function returns `NaN`', opts, function test( t ) {
 	var v = gamma( NaN );
 	t.strictEqual( isnan( v ), true, 'returns NaN when provided a NaN' );
 	t.end();
 });
 
-tape( 'if provided `-0`, the function returns negative infinity', function test( t ) {
+tape( 'if provided `-0`, the function returns negative infinity', opts, function test( t ) {
 	var v = gamma( -0.0 );
 	t.strictEqual( v, NINF, 'returns -infinity' );
 	t.end();
 });
 
-tape( 'if provided `+0`, the function returns positive infinity', function test( t ) {
+tape( 'if provided `+0`, the function returns positive infinity', opts, function test( t ) {
 	var v = gamma( 0.0 );
 	t.strictEqual( v, PINF, 'returns +infinity' );
 	t.end();
 });
 
-tape( 'if `x > 171.6144...`, the function returns positive infinity', function test( t ) {
+tape( 'if `x > 171.6144...`, the function returns positive infinity', opts, function test( t ) {
 	var values = incrspace( 172.0, 1000.0, 10.1234 );
 	var v;
 	var i;
@@ -94,7 +102,7 @@ tape( 'if `x > 171.6144...`, the function returns positive infinity', function t
 	t.end();
 });
 
-tape( 'if `x < -170.56749...`, the function returns positive infinity', function test( t ) {
+tape( 'if `x < -170.56749...`, the function returns positive infinity', opts, function test( t ) {
 	var values = incrspace( -170.57, -1000.0, -10.1234 );
 	var v;
 	var i;
@@ -106,7 +114,7 @@ tape( 'if `x < -170.56749...`, the function returns positive infinity', function
 	t.end();
 });
 
-tape( 'the function evaluates the gamma function (positive integers)', function test( t ) {
+tape( 'the function evaluates the gamma function (positive integers)', opts, function test( t ) {
 	var delta;
 	var tol;
 	var v;
@@ -121,7 +129,7 @@ tape( 'the function evaluates the gamma function (positive integers)', function
 	t.end();
 });
 
-tape( 'the function evaluates the gamma function (decimal values)', function test( t ) {
+tape( 'the function evaluates the gamma function (decimal values)', opts, function test( t ) {
 	var delta;
 	var tol;
 	var v;
@@ -136,7 +144,7 @@ tape( 'the function evaluates the gamma function (decimal values)', function tes
 	t.end();
 });
 
-tape( 'if provided a positive integer, the function returns the factorial of (n-1)', function test( t ) {
+tape( 'if provided a positive integer, the function returns the factorial of (n-1)', opts, function test( t ) {
 	t.strictEqual( gamma( 4.0 ), 6.0, 'returns 6' );
 	t.strictEqual( gamma( 5.0 ), 24.0, 'returns 24' );
 	t.strictEqual( gamma( 6.0 ), 120.0, 'returns 120' );