tests: another test for adding a new api path to an existing library (#2676)

As a follow up to #2666,
this PR adds another test case to check that a new API path can be added
to an existing library in state.yaml. The test case added in #2666 did
not have any API paths in the existing library. See the snippet below
where there is no API path in the existing library.


https://github.com/googleapis/librarian/blob/50046f559ee7cdcc4115ae790c7218a09c7fd9ae/internal/librarian/generate_command_test.go#L1572-L1584

For completeness and to avoid regressions, we should also test that new
paths can be added to an existing library which already has API paths.
This PR adds the missing test case.

---------

Signed-off-by: Anthonios Partheniou <[email protected]>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: parthea

internal/librarian/generate_command_test.go

@@ -1570,7 +1570,7 @@ func TestNeedsConfigure(t *testing.T) {
 			want:    true,
 		},
 		{
-			name:    "api and library set, library exists",
+			name:    "api and library set library exists no api path in state yaml",
 			api:     "some/api",
 			library: "some-library",
 			state: &config.LibrarianState{
@@ -1582,6 +1582,22 @@ func TestNeedsConfigure(t *testing.T) {
 			},
 			want: true,
 		},
+		{
+			name:    "api and library set library exists different api path in state yaml",
+			api:     "some/api",
+			library: "some-library",
+			state: &config.LibrarianState{
+				Libraries: []*config.LibraryState{
+					{
+						ID: "some-library",
+						APIs: []*config.API{
+							{Path: "another/api"},
+						},
+					},
+				},
+			},
+			want: true,
+		},
 		{
 			name:    "api not set",
 			api:     "",