chore: fix broken links in DEVELOPMENT.MD (#3797)

Author: zhumin8

DEVELOPMENT.md

@@ -44,7 +44,7 @@ for gapic-generator-java's Bazel build.
 There are 4 layers of testing in this repo:
 1. Traditional unit tests. These tests usually focus on testing one very specific test case at a time. For example, [MethodTest](https://github.com/googleapis/sdk-platform-java/blob/main/gapic-generator-java/src/test/java/com/google/api/generator/gapic/model/MethodTest.java) 
 2. Golden unit tests. These tests start with a test proto, we create different test cases in the proto, load the proto in unit tests and save the generated file as golden files. For example, [routing header proto](https://github.com/googleapis/sdk-platform-java/blob/main/gapic-generator-java/src/test/proto/explicit_dynamic_routing_header_testing.proto) -> Load in the [unit test](https://github.com/googleapis/sdk-platform-java/blob/main/gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpc/GrpcServiceStubClassComposerTest.java#L56-L64) -> Saved as [golden](https://github.com/googleapis/sdk-platform-java/blob/main/gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpc/goldens/GrpcRoutingHeadersStub.golden)    
-3. Showcase integration tests. They test the generated library's behavior against a mock server, see [README.md](https://github.com/googleapis/sdk-platform-java/blob/main/showcase/README.md) of showcase module for details.
+3. Showcase integration tests. They test the generated library's behavior against a mock server, see [README.md](https://github.com/googleapis/sdk-platform-java/blob/main/java-showcase/README.md) of showcase module for details.
 4. Golden integration tests. These tests generate a full client library with real protos from googleapis, for example, golden integration tests for [compute](https://github.com/googleapis/sdk-platform-java/tree/main/test/integration/goldens/compute). However, we _should_ stop adding new ones, and rely on golden unit tests and showcase tests.
 
 Based on where the code changes are, we should add different tests, in general
@@ -60,7 +60,7 @@ Based on where the code changes are, we should add different tests, in general
 
 See the [Unit Tests](https://github.com/googleapis/sdk-platform-java/blob/main/gapic-generator-java/DEVELOPMENT.md#unit-tests) section in gapic-generator-java/DEVELOPMENT.md for how to run traditional and golden unit tests.
 
-See [Running the Integration Tests](https://github.com/googleapis/sdk-platform-java/blob/main/showcase/README.md#running-the-integration-tests) and [Update the Golden Showcase Files](https://github.com/googleapis/sdk-platform-java/blob/main/showcase/README.md#update-the-golden-showcase-files) sections in showcase/README.md for how to run and update showcase integration tests.
+See [Running the Integration Tests](https://github.com/googleapis/sdk-platform-java/blob/main/java-showcase/README.md#running-the-integration-tests) and [Update the Golden Showcase Files](https://github.com/googleapis/sdk-platform-java/blob/main/java-showcase/README.md#update-the-golden-showcase-files) sections in java-showcase/README.md for how to run and update showcase integration tests.
 
 See the [Integration Tests](https://github.com/googleapis/sdk-platform-java/blob/main/gapic-generator-java/DEVELOPMENT.md#integration-tests) section in gapic-generator-java/DEVELOPMENT.md for how to run golden integration tests.