Fix #455: Improve Html parser tests (#5589)

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check off every point from the Essential Checklist! -->
## Explanation
Fix #455
- `testHtmlContentReplace_removesUnwantedNewlines`: Ensures that
unwanted newlines are removed from HTML content when parsed.
- `testHtmlContent_withImageTag_trimsLeadingAndTrailingNewlines`:
Verifies that leading and trailing newlines are trimmed from HTML
content containing an image tag.

## Essential Checklist
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- [x] The PR title and explanation each start with "Fix #bugnum: " (If
this PR fixes part of an issue, prefix the title with "Fix part of
#bugnum: ...".)
- [x] Any changes to
[scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets)
files have their rationale included in the PR explanation.
- [x] The PR follows the [style
guide](https://github.com/oppia/oppia-android/wiki/Coding-style-guide).
- [x] The PR does not contain any unnecessary code changes from Android
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app/src/sharedTest/java/org/oppia/android/app/parser/HtmlParserTest.kt

@@ -427,6 +427,57 @@ class HtmlParserTest {
     assertThat(htmlResult.toString()).endsWith(" ")
   }
 
+  @Test
+  fun testHtmlContentParsing_removesUnwantedNewlines() {
+    val htmlParser = htmlParserFactory.create(
+      resourceBucketName,
+      entityType = "",
+      entityId = "",
+      imageCenterAlign = true,
+      displayLocale = appLanguageLocaleHandler.getDisplayLocale()
+    )
+    val (_, htmlResult) = activityScenarioRule.scenario.runWithActivity {
+      val textView: TextView = it.findViewById(R.id.test_html_content_text_view)
+      val htmlResult = htmlParser.parseOppiaHtml(
+        "<ul><li>\n\tThe counting numbers (1, 2, 3, 4, 5 ….)\n\n</li><li>\n\tHow to tell" +
+          " whether one counting number is bigger or smaller than another.\n\n</li></ul>",
+        textView
+      )
+      textView.text = htmlResult
+      return@runWithActivity textView to htmlResult
+    }
+
+    assertThat(htmlResult.toString()).isEqualTo(
+      "The counting numbers (1, 2, 3, 4, 5 ….)\nHow to tell whether one counting " +
+        "number is bigger or smaller than another"
+    )
+  }
+
+  @Test
+  fun testHtmlContentParsing_withImageTag_trimsLeadingAndTrailingNewlines() {
+    val htmlParser = htmlParserFactory.create(
+      resourceBucketName,
+      entityType = "",
+      entityId = "",
+      imageCenterAlign = true,
+      displayLocale = appLanguageLocaleHandler.getDisplayLocale()
+    )
+    val htmlResult = activityScenarioRule.scenario.runWithActivity {
+      val textView: TextView = it.findViewById(R.id.test_html_content_text_view)
+      return@runWithActivity htmlParser.parseOppiaHtml(
+        "\n<oppia-noninteractive-image filepath-with-value=\"test.png\">" +
+          "</oppia-noninteractive-image>\n",
+        textView
+      )
+    }
+    val imageSpans = htmlResult.getSpansFromWholeString(ImageSpan::class)
+    assertThat(imageSpans).hasLength(1)
+    assertThat(imageSpans.first().source).isEqualTo("test.png")
+
+    assertThat(htmlResult.toString().startsWith("\n")).isFalse()
+    assertThat(htmlResult.toString().endsWith("\n")).isFalse()
+  }
+
   @Test
   fun testHtmlContent_changeDeviceToLtr_textViewDirectionIsSetToLtr() {
     val htmlParser = htmlParserFactory.create(