Function that finds container with a specific ID.

container/traversal.go

@@ -14,6 +14,11 @@
 
 package container
 
+import (
+	"errors"
+	"fmt"
+)
+
 // traversal.go provides functions that navigate the container tree.
 
 // rootCont returns the root container.
@@ -56,3 +61,26 @@ func postOrder(c *Container, errStr *string, visit visitFunc) {
 		return
 	}
 }
+
+// findID finds container with the provided ID.
+// Returns an error of there is no container with the specified ID.
+func findID(root *Container, id string) (*Container, error) {
+	if id == "" {
+		return nil, errors.New("the container ID must not be empty")
+	}
+
+	var (
+		errStr string
+		cont   *Container
+	)
+	preOrder(root, &errStr, visitFunc(func(c *Container) error {
+		if c.opts.id == id {
+			cont = c
+		}
+		return nil
+	}))
+	if cont == nil {
+		return nil, fmt.Errorf("cannot find container with ID %q", id)
+	}
+	return cont, nil
+}

container/traversal_test.go

@@ -165,3 +165,63 @@ func TestTraversal(t *testing.T) {
 		})
 	}
 }
+
+func TestFindID(t *testing.T) {
+	tests := []struct {
+		desc      string
+		container func(ft *faketerm.Terminal) (*Container, error)
+		id        string
+		wantFound bool
+		wantErr   bool
+	}{
+		{
+			desc: "fails when searching with empty ID",
+			container: func(ft *faketerm.Terminal) (*Container, error) {
+				return New(ft)
+			},
+			wantErr: true,
+		},
+		{
+			desc: "no container with the specified ID",
+			container: func(ft *faketerm.Terminal) (*Container, error) {
+				return New(ft)
+			},
+			id:      "mycont",
+			wantErr: true,
+		},
+		{
+			desc: "finds the container",
+			container: func(ft *faketerm.Terminal) (*Container, error) {
+				return New(ft, ID("mycont"))
+			},
+			id:        "mycont",
+			wantFound: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.desc, func(t *testing.T) {
+			ft, err := faketerm.New(image.Point{10, 10})
+			if err != nil {
+				t.Fatalf("faketerm.New => unexpected error: %v", err)
+			}
+
+			cont, err := tc.container(ft)
+			if err != nil {
+				t.Fatalf("tc.container => unexpected error: %v", err)
+			}
+
+			got, err := findID(cont, tc.id)
+			if (err != nil) != tc.wantErr {
+				t.Errorf("findID => unexpected error: %v, wantErr: %v", err, tc.wantErr)
+			}
+			if err != nil {
+				return
+			}
+
+			if (got != nil) != tc.wantFound {
+				t.Errorf("findID returned %v, wantFound: %v", got, tc.wantFound)
+			}
+		})
+	}
+}