Make tests for URL load check rule functions self contained

Several rules check whether URLs provided in project metadata load.

Previously, the handling of various HTTP response status codes of these rule functions was tested by using the
convenient httpstat.us site. Unfortunately the maintainers of that site shut it down months ago due to abuse. This
caused the spurious failure of the unit tests. Although the httpstat.us maintainers state that they plan to eventually
resume service, there hasn't been any indication of progress on that front.

So it will be best to make the tests self contained, without any dependence on an external site. This is accomplished by
creating a local HTTP server that responds with the intended status code. Unfortunately this does require the addition
of code to the test in order to generate test data on the fly in order to reference the arbitrary port of the test
server.

Author: per1234

internal/rule/rulefunction/library_test.go

@@ -18,16 +18,20 @@ package rulefunction
 
 import (
 	"fmt"
+	"net/http"
 	"os"
 	"regexp"
+	"strings"
 	"testing"
 	"time"
 
 	"github.com/arduino/arduino-lint/internal/project"
 	"github.com/arduino/arduino-lint/internal/project/projectdata"
 	"github.com/arduino/arduino-lint/internal/project/projecttype"
 	"github.com/arduino/arduino-lint/internal/rule/ruleresult"
+	"github.com/arduino/arduino-lint/internal/util/test"
 	"github.com/arduino/go-paths-helper"
+	"github.com/arduino/go-properties-orderedmap"
 	"github.com/go-git/go-git/v5"
 	"github.com/go-git/go-git/v5/plumbing/object"
 	"github.com/stretchr/testify/assert"
@@ -780,11 +784,75 @@ func TestLibraryPropertiesUrlFieldDeadLink(t *testing.T) {
 		{"Unable to load", "InvalidLibraryProperties", ruleresult.NotRun, ""},
 		{"Not defined", "MissingFields", ruleresult.NotRun, ""},
 		{"Bad URL", "BadURL", ruleresult.Fail, "^Head \"http://invalid/\": dial tcp: lookup invalid"},
-		{"HTTP error 404", "URL404", ruleresult.Fail, "^404 Not Found$"},
-		{"Good URL", "Recursive", ruleresult.Pass, ""},
 	}
 
 	checkLibraryRuleFunction(LibraryPropertiesURLFieldDeadLink, testTables, t)
+
+	/*
+		In order to avoid a dependency on an external site, a test HTTP server is used for the tests covering handling of
+		various HTTP response status codes. For this reason, the following tests can't be performed via the
+		checkLibraryRuleFunction function.
+	*/
+	statusTestTables := []struct {
+		testName            string
+		serverStatus        int
+		expectedRuleResult  ruleresult.Type
+		expectedOutputQuery string
+	}{
+		{"HTTP error 404", http.StatusNotFound, ruleresult.Fail, "^404 Not Found$"},
+		{"Good URL", http.StatusOK, ruleresult.Pass, ""},
+	}
+
+	var propertiesMap = map[string]string{
+		"name":          "WebServer",
+		"version":       "1.0.0",
+		"author":        "Cristian Maglie <[email protected]>, Pippo Pluto <[email protected]>",
+		"maintainer":    "Cristian Maglie <[email protected]>",
+		"sentence":      "A library that makes coding a Webserver a breeze.",
+		"paragraph":     "Supports HTTP1.1 and you can do GET and POST.",
+		"category":      "Communication",
+		"architectures": "avr",
+	}
+
+	libraryProperties := properties.NewFromHashmap(propertiesMap)
+
+	for _, testTable := range statusTestTables {
+		// Create an HTTP server that will return the desired status.
+		server := test.StatusServer(testTable.serverStatus)
+		defer server.Close()
+
+		libraryProperties.Set("url", server.URL)
+		// AsSlice is the closest thing to a []byte output function provided by
+		// `github.com/arduino/go-properties-orderedmap`.
+		propertiesBytes := []byte(strings.Join(libraryProperties.AsSlice(), "\n"))
+
+		// Generate the test data library.
+		sourcePath := librariesTestDataPath.Join("TestLibraryPropertiesUrlFieldDeadLink")
+		tempPath, err := paths.MkTempDir("", "TestLibraryPropertiesUrlFieldDeadLink")
+		defer tempPath.RemoveAll() // Clean up after the test.
+		require.NoError(t, err)
+		libraryPath := tempPath.Join("TestLibraryPropertiesUrlFieldDeadLink")
+		err = sourcePath.CopyDirTo(libraryPath)
+		require.NoError(t, err)
+		err = libraryPath.Join("library.properties").WriteFile(propertiesBytes)
+		require.NoError(t, err)
+
+		testProject := project.Type{
+			Path:             libraryPath,
+			ProjectType:      projecttype.Library,
+			SuperprojectType: projecttype.Library,
+		}
+		projectdata.Initialize(testProject)
+
+		result, output := LibraryPropertiesURLFieldDeadLink()
+		assert.Equal(t, testTable.expectedRuleResult, result, testTable.testName)
+		expectedOutputRegexp := regexp.MustCompile(testTable.expectedOutputQuery)
+		assert.True(
+			t,
+			expectedOutputRegexp.MatchString(output),
+			fmt.Sprintf("%s (output: %s, assertion regex: %s)", testTable.testName, output, testTable.expectedOutputQuery),
+		)
+	}
 }
 
 func TestLibraryPropertiesArchitecturesFieldMissing(t *testing.T) {