Create MockResolver and use to improve python cataloger tests

Signed-off-by: Dan Luhring <dan.luhring@anchore.com>

syft/source/mock_resolver.go

@@ -0,0 +1,115 @@
+package source
+
+import (
+	"fmt"
+	"github.com/anchore/syft/internal/file"
+	"io/ioutil"
+	"os"
+)
+
+var _ Resolver = (*MockResolver)(nil)
+
+// MockResolver implements the Resolver interface and is intended for use *only in test code*.
+// It provides an implementation that can resolve local filesystem paths using only a provided discrete list of file
+// paths, which are typically paths to test fixtures.
+type MockResolver struct {
+	Locations []Location
+}
+
+// NewMockResolverForPaths creates a new MockResolver, where the only resolvable
+// files are those specified by the supplied paths.
+func NewMockResolverForPaths(paths ...string) *MockResolver {
+	var locations []Location
+	for _, p := range paths {
+		locations = append(locations, NewLocation(p))
+	}
+
+	return &MockResolver{Locations: locations}
+}
+
+// String returns the string representation of the MockResolver.
+func (r MockResolver) String() string {
+	return fmt.Sprintf("mock:(%s,...)", r.Locations[0].Path)
+}
+
+// FileContentsByLocation fetches file contents for a single location. If the
+// path does not exist, an error is returned.
+func (r MockResolver) FileContentsByLocation(location Location) (string, error) {
+	for _, l := range r.Locations {
+		if l == location {
+			return stringContent(location.Path)
+		}
+	}
+
+	return "", fmt.Errorf("no file for location: %v", location)
+}
+
+// MultipleFileContentsByLocation returns the file contents for all specified Locations.
+func (r MockResolver) MultipleFileContentsByLocation(locations []Location) (map[Location]string, error) {
+	results := make(map[Location]string)
+	for _, l := range locations {
+		contents, err := r.FileContentsByLocation(l)
+		if err != nil {
+			return nil, err
+		}
+		results[l] = contents
+	}
+
+	return results, nil
+}
+
+// FilesByPath returns all Locations that match the given paths.
+func (r MockResolver) FilesByPath(paths ...string) ([]Location, error) {
+	var results []Location
+	for _, p := range paths {
+		for _, location := range r.Locations {
+			if p == location.Path {
+				results = append(results, NewLocation(p))
+			}
+		}
+	}
+
+	return results, nil
+}
+
+// FilesByGlob returns all Locations that match the given path glob pattern.
+func (r MockResolver) FilesByGlob(patterns ...string) ([]Location, error) {
+	var results []Location
+	for _, pattern := range patterns {
+		for _, location := range r.Locations {
+			if file.GlobMatch(pattern, location.Path) {
+				results = append(results, location)
+			}
+		}
+	}
+
+	return results, nil
+}
+
+// RelativeFileByPath returns a single Location for the given path.
+func (r MockResolver) RelativeFileByPath(_ Location, path string) *Location {
+	paths, err := r.FilesByPath(path)
+	if err != nil {
+		return nil
+	}
+
+	if len(paths) < 1 {
+		return nil
+	}
+
+	return &paths[0]
+}
+
+func stringContent(path string) (string, error) {
+	reader, err := os.Open(path)
+	if err != nil {
+		return "", err
+	}
+
+	b, err := ioutil.ReadAll(reader)
+	if err != nil {
+		return "", err
+	}
+
+	return string(b), nil
+}