Writing a test for the /blog/update endpoint

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**Is your feature request related to a problem? Please describe.**
The /blog/update endpoint is in need of a unit test.

**Describe the solution you'd like**
Write a test that successfully updates already existing information inside of the database to something new.

**Additional context**
This is a test written inside of BlogTests.Java to test the @PostMapping /blogs endpoint.

```
@Test
public void postBlogs_SavesBlogToDatabase() throws Exception {
blogTestsUtil.tearDown();
Blog blog1 = new Blog("Our Very First Blog Post", "This is an actual Subheader", "An Actual Image", "This body has things we actually care about");
MockMultipartFile firstFile = new MockMultipartFile("image", "filename.txt", "text/plain", "some xml".getBytes());
MvcResult result = mockMvc.perform(multipart("/blogs").file(firstFile).param("blogData", objectMapper.writeValueAsString(blog1)))
.andDo(print())
.andExpect(status().isOk())
.andExpect(jsonPath("$.header").value("Our Very First Blog Post"))
.andReturn();
assertEquals(1, blogRepository.findAll().size());
blogTestsUtil.tearDown();
}
```

Start with BlogTests.Java and the existing postBlogs_SavesBlogToDatabase test to understand the test setup and database cleanup. Confirm whether the intended target is /blog/update or the /blogs endpoint shown in the context, then cover updating existing database information and verify the updated result and persistence.

Written by the indexing model from the issue text.