[go-migration] Refactor common context, generate mocks, fix hollow unit tests for supply/finalize (#1177)

[go-migration] Refactor context to interfaces and fix hollow unit tests for supply/finalize
Introduces Go interfaces (Stager, Manifest, Installer, Command) in the
common context to replace concrete libbuildpack types, enabling mock
generation via gomock. Previously, the supply and finalize unit tests
always passed vacuously — this PR rewrites them to actually exercise
`supply.Run()` and `finalize.Run()` for Tomcat, Spring Boot, and Groovy
containers using generated mocks, without performing real dependency
downloads. Adds a new finalize test case for the Groovy container.
Also consolidates the `Installer` interface from `cf_metrics_exporter`
into the shared common context and fixes related test setup.
Fixes #1172

Author: kiril-keranov

go.mod

@@ -6,9 +6,11 @@ require (
 	github.com/Dynatrace/libbuildpack-dynatrace v1.8.0
 	github.com/cloudfoundry/libbuildpack v0.0.0-20251203175254-7be530ec9fef
 	github.com/cloudfoundry/switchblade v0.9.4
+	github.com/golang/mock v1.6.0
 	github.com/onsi/ginkgo/v2 v2.27.2
 	github.com/onsi/gomega v1.38.2
 	github.com/sclevine/spec v1.4.0
+	go.yaml.in/yaml/v3 v3.0.4
 	gopkg.in/yaml.v2 v2.4.0
 )
 
@@ -42,7 +44,6 @@ require (
 	go.opentelemetry.io/otel v1.32.0 // indirect
 	go.opentelemetry.io/otel/metric v1.32.0 // indirect
 	go.opentelemetry.io/otel/trace v1.32.0 // indirect
-	go.yaml.in/yaml/v3 v3.0.4 // indirect
 	golang.org/x/mod v0.30.0 // indirect
 	golang.org/x/net v0.47.0 // indirect
 	golang.org/x/sync v0.18.0 // indirect

src/internal/mocks/mocks.go

@@ -4,20 +4,49 @@ import (
 	"encoding/json"
 	"fmt"
 	"github.com/cloudfoundry/libbuildpack"
+	"io"
 	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 )
 
+//go:generate mockgen -source=context.go --destination=../../internal/mocks/mocks.go --package=mocks
+
+type Command interface {
+	Execute(string, io.Writer, io.Writer, string, ...string) error
+}
+
+type Stager interface {
+	LinkDirectoryInDepDir(string, string) error
+	BuildDir() string
+	DepDir() string
+	DepsIdx() string
+	CacheDir() string
+	WriteConfigYml(interface{}) error
+	WriteEnvFile(string, string) error
+	WriteProfileD(string, string) error
+}
+
+type Manifest interface {
+	AllDependencyVersions(string) []string
+	DefaultVersion(string) (libbuildpack.Dependency, error)
+	GetEntry(libbuildpack.Dependency) (*libbuildpack.ManifestEntry, error)
+}
+
+type Installer interface {
+	InstallDependency(libbuildpack.Dependency, string) error
+	InstallDependencyWithStrip(libbuildpack.Dependency, string, int) error
+}
+
 // Context holds shared dependencies for buildpack components
 // Used by containers, frameworks, and JREs to access buildpack infrastructure
 type Context struct {
-	Stager    *libbuildpack.Stager
-	Manifest  *libbuildpack.Manifest
-	Installer *libbuildpack.Installer
+	Stager    Stager
+	Manifest  Manifest
+	Installer Installer
 	Log       *libbuildpack.Logger
-	Command   *libbuildpack.Command
+	Command   Command
 }
 
 // DetermineJavaVersion determines the major Java version from a Java installation