test(math/base/special/cosm1): add tests for signed zeros

---
type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes.
report:
  - task: lint_filenames
    status: passed
  - task: lint_editorconfig
    status: passed
  - task: lint_markdown
    status: na
  - task: lint_package_json
    status: na
  - task: lint_repl_help
    status: na
  - task: lint_javascript_src
    status: na
  - task: lint_javascript_cli
    status: na
  - task: lint_javascript_examples
    status: na
  - task: lint_javascript_tests
    status: passed
  - task: lint_javascript_benchmarks
    status: na
  - task: lint_python
    status: na
  - task: lint_r
    status: na
  - task: lint_c_src
    status: na
  - task: lint_c_examples
    status: na
  - task: lint_c_benchmarks
    status: na
  - task: lint_c_tests_fixtures
    status: na
  - task: lint_shell
    status: na
  - task: lint_typescript_declarations
    status: passed
  - task: lint_typescript_tests
    status: na
  - task: lint_license_headers
    status: passed
---

Author: Payal-Goswami

lib/node_modules/@stdlib/math/base/special/cosm1/test/test.js

@@ -51,6 +51,19 @@ tape( 'main export is a function', function test( t ) {
 	t.end();
 });
 
+tape( 'the function returns positive zero for zero and negative zero', function test( t ) {
+	var v1 = cosm1( 0.0 );
+	var v2 = cosm1( -0.0 );
+
+	t.strictEqual( v1, 0.0, 'returns +0 for +0' );
+	t.strictEqual( 1.0/v1, PINF, 'returns +0 (not -0)' );
+
+	t.strictEqual( v2, 0.0, 'returns +0 for -0' );
+	t.strictEqual( 1.0/v2, PINF, 'returns +0 (not -0)' );
+
+	t.end();
+});
+
 tape( 'the function computes the cosine minus one more accurately inside the interval [-π/4,π/4]', function test( t ) {
 	var expected;
 	var x;