public function testProperlyCompilesRequestHeaders()
 {
     $headers = $this->curlClient->compileRequestHeaders([]);
     $expectedHeaders = [];
     $this->assertEquals($expectedHeaders, $headers);
     $headers = $this->curlClient->compileRequestHeaders(['X-foo' => 'bar']);
     $expectedHeaders = ['X-foo: bar'];
     $this->assertEquals($expectedHeaders, $headers);
 }