t: Add 3 traceparent header tests

The new `traceparent` header auto-injection from
`ngx.var.http_traceparent` has to be tested.

So add a new file `t/21-traceparent-header.t` containing 3 tests
for that:
* TEST 1: No traceparent header is set
* TEST 2: The traceparent header is correctly added when
          ngx.var.http_traceparent is used
* TEST 3: The traceparent header is not modified from
          ngx.var.http_traceparent if it is already set

Use an NGINX directive `set $http_traceparent '00-000...-01';` in
front of the LUA block to emulate `nginx-otel` behavior.

The case that there is a `traceparent` header added with
`request_uri()` and `ngx.var.http_traceparent` is not set, is already
covered by tests 1 and 3.

Author: sriemer

t/21-traceparent-header.t

@@ -0,0 +1,92 @@
+use Test::Nginx::Socket 'no_plan';
+use Cwd qw(cwd);
+
+my $pwd = cwd();
+
+$ENV{TEST_NGINX_RESOLVER} = '8.8.8.8';
+$ENV{TEST_NGINX_PWD} ||= $pwd;
+$ENV{TEST_COVERAGE} ||= 0;
+
+our $HttpConfig = qq{
+    lua_package_path "$pwd/lib/?.lua;/usr/local/share/lua/5.1/?.lua;;";
+    error_log logs/error.log debug;
+    resolver 8.8.8.8 ipv6=off;
+
+    init_by_lua_block {
+        if $ENV{TEST_COVERAGE} == 1 then
+            jit.off()
+            require("luacov.runner").init()
+        end
+
+        require("resty.http").debug(true)
+    }
+};
+
+no_long_string();
+#no_diff();
+
+run_tests();
+
+__DATA__
+=== TEST 1: No traceparent header is set
+--- http_config eval: $::HttpConfig
+--- config
+    location /lua {
+        content_by_lua '
+            require("resty.http").debug(true)
+            local http = require "resty.http"
+            local httpc = http.new()
+
+            local res, err = httpc:request_uri("http://www.google.com")
+        ';
+    }
+--- request
+GET /lua
+--- no_error_log
+[error]
+traceparent:
+
+
+=== TEST 2: The traceparent header is correctly added when ngx.var.http_traceparent is used
+--- http_config eval: $::HttpConfig
+--- config
+    location /lua {
+        # emulate nginx-otel behavior here
+        set $http_traceparent '00-000000000000000019f4e02c82857913-11488c6e00d1d248-01';
+        content_by_lua '
+            require("resty.http").debug(true)
+            local http = require "resty.http"
+            local httpc = http.new()
+            local res, err = httpc:request_uri("http://www.google.com")
+        ';
+    }
+--- request
+GET /lua
+--- no_error_log
+[error]
+--- error_log
+traceparent: 00-000000000000000019f4e02c82857913-11488c6e00d1d248-01
+
+
+=== TEST 3: The traceparent header is not modified from ngx.var.http_traceparent if it is already set
+--- http_config eval: $::HttpConfig
+--- config
+    location /lua {
+        # emulate nginx-otel behavior here
+        set $http_traceparent '00-000000000000000019f4e02c82857913-11488c6e00d1d248-01';
+        content_by_lua '
+            require("resty.http").debug(true)
+            local http = require "resty.http"
+            local httpc = http.new()
+            local req_headers = {}
+            req_headers["traceparent"] = "00-00000000000000006633c2d00527dd33-1af98f7e6ecd16ff-01"
+            local res, err = httpc:request_uri("http://www.google.com", {method = GET, headers = req_headers})
+        ';
+    }
+--- request
+GET /lua
+--- no_error_log
+[error]
+traceparent: 00-000000000000000019f4e02c82857913-11488c6e00d1d248-01
+--- error_log
+traceparent: 00-00000000000000006633c2d00527dd33-1af98f7e6ecd16ff-01