Add more tests for Image.getOs()

See gh-45305

Signed-off-by: Johnny Lim <izeye@naver.com>

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/test/java/org/springframework/boot/buildpack/platform/docker/type/ImageTests.java

@@ -67,6 +67,18 @@ class ImageTests extends AbstractJsonTests {
 		assertThat(image.getOs()).isEqualTo("linux");
 	}
 
+	@Test
+	void getOsWhenOsIsNotDefaultOsReturnsOs() throws Exception {
+		Image image = Image.of(getContent("image-non-default-os.json"));
+		assertThat(image.getOs()).isEqualTo("windows");
+	}
+
+	@Test
+	void getOsWhenOsIsEmptyReturnsDefaultOs() throws Exception {
+		Image image = Image.of(getContent("image-empty-os.json"));
+		assertThat(image.getOs()).isEqualTo("linux");
+	}
+
 	@Test
 	void getCreatedReturnsDate() throws Exception {
 		Image image = getImage();

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/test/resources/org/springframework/boot/buildpack/platform/docker/type/image-empty-os.json

@@ -0,0 +1,30 @@
+{
+  "Id": "sha256:21635a6b4880772f3fabbf8b660907fa38636558cf787cc26f1779fc4b4e2cba",
+  "RepoTags": [
+    "ghcr.io/spring-io/spring-boot-cnb-test-builder:0.0.1"
+  ],
+  "RepoDigests": [
+    "ghcr.io/spring-io/spring-boot-cnb-test-builder@sha256:21635a6b4880772f3fabbf8b660907fa38636558cf787cc26f1779fc4b4e2cba"
+  ],
+  "Parent": "",
+  "Comment": "",
+  "DockerVersion": "",
+  "Author": "",
+  "Config": null,
+  "Architecture": "",
+  "Os": "",
+  "Size": 166797518,
+  "GraphDriver": {
+    "Data": null,
+    "Name": "overlayfs"
+  },
+  "RootFS": {},
+  "Metadata": {
+    "LastTagTime": "2025-04-10T22:41:27.520294922Z"
+  },
+  "Descriptor": {
+    "mediaType": "application/vnd.oci.image.index.v1+json",
+    "digest": "sha256:21635a6b4880772f3fabbf8b660907fa38636558cf787cc26f1779fc4b4e2cba",
+    "size": 513
+  }
+}

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/test/resources/org/springframework/boot/buildpack/platform/docker/type/image-non-default-os.json

@@ -0,0 +1,30 @@
+{
+  "Id": "sha256:21635a6b4880772f3fabbf8b660907fa38636558cf787cc26f1779fc4b4e2cba",
+  "RepoTags": [
+    "ghcr.io/spring-io/spring-boot-cnb-test-builder:0.0.1"
+  ],
+  "RepoDigests": [
+    "ghcr.io/spring-io/spring-boot-cnb-test-builder@sha256:21635a6b4880772f3fabbf8b660907fa38636558cf787cc26f1779fc4b4e2cba"
+  ],
+  "Parent": "",
+  "Comment": "",
+  "DockerVersion": "",
+  "Author": "",
+  "Config": null,
+  "Architecture": "",
+  "Os": "windows",
+  "Size": 166797518,
+  "GraphDriver": {
+    "Data": null,
+    "Name": "overlayfs"
+  },
+  "RootFS": {},
+  "Metadata": {
+    "LastTagTime": "2025-04-10T22:41:27.520294922Z"
+  },
+  "Descriptor": {
+    "mediaType": "application/vnd.oci.image.index.v1+json",
+    "digest": "sha256:21635a6b4880772f3fabbf8b660907fa38636558cf787cc26f1779fc4b4e2cba",
+    "size": 513
+  }
+}