Add dnfjson mock data package and cmd

The cases are directly copied (or lightly adapted) from
rpmmd_mock/fixtures.

The purpose of the mocks/dnfjson package is to create files with data
for testing the dnfjson package without the need to call the dnf-json
script.  Each public function creates a file with test responses in the
same format as the dnf-json script's responses (either valid results or
errors).  The dnfjson.Solver can be configured to call the new
./cmd/mock-dnf-json program with the test data file as an argument and a
valid dnf-json request for input.  The mock-dnf-json checks the input
request for unknown fields before responding with the contents of the
file.

Each test case file contains two responses, one for each command
supported by dnf-json: "depsolve" and "dump".  mock-dnf-json responds
with the appropriate data based on the command in the request.  This is
necessary for tests that require both commands in the same call, e.g.,
tests of the weldr API's moduleInfoHandler() which fetches a package
list and then needs to depsolve a subset of those packages.

There are also cases when we want one of the two responses to be an
error.  The mock-dnf-json program will return with an error code if it
can successfully unmarshal the intended response into the dnfjson.Error
type.

internal/mocks/dnfjson/dnfjson.go

@@ -0,0 +1,203 @@
+// dnfjson_mock provides data and methods for testing the dnfjson package.
+package dnfjson_mock
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/osbuild/osbuild-composer/internal/dnfjson"
+	"github.com/osbuild/osbuild-composer/internal/rpmmd"
+)
+
+func generatePackageList() rpmmd.PackageList {
+	baseTime, err := time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+
+	if err != nil {
+		panic(err)
+	}
+
+	var packageList rpmmd.PackageList
+
+	for i := 0; i < 22; i++ {
+		basePackage := rpmmd.Package{
+			Name:        fmt.Sprintf("package%d", i),
+			Summary:     fmt.Sprintf("pkg%d sum", i),
+			Description: fmt.Sprintf("pkg%d desc", i),
+			URL:         fmt.Sprintf("https://pkg%d.example.com", i),
+			Epoch:       0,
+			Version:     fmt.Sprintf("%d.0", i),
+			Release:     fmt.Sprintf("%d.fc30", i),
+			Arch:        "x86_64",
+			BuildTime:   baseTime.AddDate(0, i, 0),
+			License:     "MIT",
+		}
+
+		secondBuild := basePackage
+
+		secondBuild.Version = fmt.Sprintf("%d.1", i)
+		secondBuild.BuildTime = basePackage.BuildTime.AddDate(0, 0, 1)
+
+		packageList = append(packageList, basePackage, secondBuild)
+	}
+
+	return packageList
+}
+
+func createBaseDepsolveFixture() []dnfjson.PackageSpec {
+	return []dnfjson.PackageSpec{
+		{
+			Name:    "dep-package3",
+			Epoch:   7,
+			Version: "3.0.3",
+			Release: "1.fc30",
+			Arch:    "x86_64",
+			RepoID:  "0",
+		},
+		{
+			Name:    "dep-package1",
+			Epoch:   0,
+			Version: "1.33",
+			Release: "2.fc30",
+			Arch:    "x86_64",
+			RepoID:  "0",
+		},
+		{
+			Name:    "dep-package2",
+			Epoch:   0,
+			Version: "2.9",
+			Release: "1.fc30",
+			Arch:    "x86_64",
+			RepoID:  "0",
+		},
+	}
+}
+
+// BaseDeps is the expected list of dependencies (as rpmmd.PackageSpec) from
+// the Base ResponseGenerator
+func BaseDeps() []rpmmd.PackageSpec {
+	return []rpmmd.PackageSpec{
+		{
+			Name:     "dep-package3",
+			Epoch:    7,
+			Version:  "3.0.3",
+			Release:  "1.fc30",
+			Arch:     "x86_64",
+			CheckGPG: true,
+		},
+		{
+			Name:     "dep-package1",
+			Epoch:    0,
+			Version:  "1.33",
+			Release:  "2.fc30",
+			Arch:     "x86_64",
+			CheckGPG: true,
+		},
+		{
+			Name:     "dep-package2",
+			Epoch:    0,
+			Version:  "2.9",
+			Release:  "1.fc30",
+			Arch:     "x86_64",
+			CheckGPG: true,
+		},
+	}
+}
+
+type ResponseGenerator func(string) string
+
+func Base(tmpdir string) string {
+	deps := map[string]interface{}{
+		"checksums": map[string]string{
+			"0": "test:responsechecksum",
+		},
+		"dependencies": createBaseDepsolveFixture(),
+	}
+
+	pkgs := map[string]interface{}{
+		"checksums": map[string]string{
+			"0": "test:responsechecksum",
+		},
+		"packages": generatePackageList(),
+	}
+
+	data := map[string]interface{}{
+		"depsolve": deps,
+		"dump":     pkgs,
+	}
+	path := filepath.Join(tmpdir, "base.json")
+	write(data, path)
+	return path
+}
+
+func NonExistingPackage(tmpdir string) string {
+	deps := dnfjson.Error{
+		Kind:   "MarkingErrors",
+		Reason: "Error occurred when marking packages for installation: Problems in request:\nmissing packages: fash",
+	}
+	data := map[string]interface{}{
+		"depsolve": deps,
+	}
+	path := filepath.Join(tmpdir, "notexist.json")
+	write(data, path)
+	return path
+}
+
+func BadDepsolve(tmpdir string) string {
+	deps := dnfjson.Error{
+		Kind:   "DepsolveError",
+		Reason: "There was a problem depsolving ['go2rpm']: \n Problem: conflicting requests\n  - nothing provides askalono-cli needed by go2rpm-1-4.fc31.noarch",
+	}
+	pkgs := map[string]interface{}{
+		"checksums": map[string]string{
+			"0": "test:responsechecksum",
+		},
+		"packages": generatePackageList(),
+	}
+
+	data := map[string]interface{}{
+		"depsolve": deps,
+		"dump":     pkgs,
+	}
+	path := filepath.Join(tmpdir, "baddepsolve.json")
+	write(data, path)
+	return path
+}
+
+func BadFetch(tmpdir string) string {
+	deps := dnfjson.Error{
+		Kind:   "DepsolveError",
+		Reason: "There was a problem depsolving ['go2rpm']: \n Problem: conflicting requests\n  - nothing provides askalono-cli needed by go2rpm-1-4.fc31.noarch",
+	}
+	pkgs := dnfjson.Error{
+		Kind:   "FetchError",
+		Reason: "There was a problem when fetching packages.",
+	}
+	data := map[string]interface{}{
+		"depsolve": deps,
+		"dump":     pkgs,
+	}
+	path := filepath.Join(tmpdir, "badfetch.json")
+	write(data, path)
+	return path
+}
+
+func marshal(data interface{}) []byte {
+	jdata, err := json.Marshal(data)
+	if err != nil {
+		panic(err)
+	}
+	return jdata
+}
+
+func write(data interface{}, path string) {
+	fp, err := os.Create(path)
+	if err != nil {
+		panic(err)
+	}
+	if _, err := fp.Write(marshal(data)); err != nil {
+		panic(err)
+	}
+}