Add test for getExtension method in Embedding class (#1134)

- Introduce a new test case to ensure correct behavior of the getExtension method.
- Enhance coverage for the Embedding class, specifically validating its handling of unknown MIME types.

Co-authored-by: Harshpreet Singh <Harshpreet.Singh@dal.ca>

src/test/java/net/masterthought/cucumber/json/EmbeddingTest.java

@@ -133,6 +133,23 @@ public void getExtension_ReturnsFileExtension() {
         assertThat(actualExtension).isEqualTo(this.fileName.split("\\.")[1]);
     }
 
+    @Test
+    public void getExtension_UsesExtensionFromNameWhenMIMETypeIsUnknown() {
+        // Arrange
+        String mimeType = "unknown/mimetype";
+        String data = "c29tZSBkYXRh";
+        String name = "example.docx";
+
+        // Creating an embedding here with an unknown MIME type and a name containing a file extension
+        Embedding embedding = new Embedding(mimeType, data, name);
+
+        // Act
+        String actualExtension = embedding.getExtension();
+
+        // Assert
+        assertThat(actualExtension).isEqualTo("docx");
+    }
+
     @Test
     public void getName_ReturnsNull() {
         // given