add unit-test class for the issue 5155 (#11217)

core-java-modules/core-java-string-operations-3/src/test/java/com/baeldung/countspaces/CountSpacesInStringUnitTest.java

@@ -0,0 +1,65 @@
+package com.baeldung.countspaces;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import org.apache.commons.lang3.StringUtils;
+import org.junit.jupiter.api.Test;
+
+class CountSpacesInStringUnitTest {
+    private static final String INPUT_STRING = "  This string has nine spaces and a Tab:'	'";
+    private static final int EXPECTED_COUNT = 9;
+
+    @Test
+    void givenString_whenCountSpaceByLooping_thenReturnsExpectedCount() {
+        int spaceCount = 0;
+        for (char c : INPUT_STRING.toCharArray()) {
+            if (c == ' ') {
+                spaceCount++;
+            }
+        }
+        assertThat(spaceCount).isEqualTo(EXPECTED_COUNT);
+    }
+
+    @Test
+    void givenString_whenCountSpaceByJava8StreamFilter_thenReturnsExpectedCount() {
+        long spaceCount = INPUT_STRING.chars().filter(c -> c == (int) ' ').count();
+        assertThat(spaceCount).isEqualTo(EXPECTED_COUNT);
+    }
+
+    @Test
+    void givenString_whenCountSpaceByRegexMatcher_thenReturnsExpectedCount() {
+        Pattern pattern = Pattern.compile(" ");
+        Matcher matcher = pattern.matcher(INPUT_STRING);
+        int spaceCount = 0;
+        while (matcher.find()) {
+            spaceCount++;
+        }
+        assertThat(spaceCount).isEqualTo(EXPECTED_COUNT);
+    }
+
+    @Test
+    void givenString_whenCountSpaceByReplaceAll_thenReturnsExpectedCount() {
+        int spaceCount = INPUT_STRING.replaceAll("[^ ]", "").length();
+        assertThat(spaceCount).isEqualTo(EXPECTED_COUNT);
+    }
+
+    @Test
+    void givenString_whenCountSpaceBySplit_thenReturnsExpectedCount() {
+        int spaceCount = INPUT_STRING.split(" ").length - 1;
+        assertThat(spaceCount).isEqualTo(EXPECTED_COUNT);
+    }
+
+    @Test
+    void givenString_whenCountSpaceUsingApacheCommons_thenReturnsExpectedCount() {
+        int spaceCount = StringUtils.countMatches(INPUT_STRING, " ");
+        assertThat(spaceCount).isEqualTo(EXPECTED_COUNT);
+    }
+
+    @Test
+    void givenString_whenCountSpaceUsingSpring_thenReturnsExpectedCount() {
+        int spaceCount = org.springframework.util.StringUtils.countOccurrencesOf(INPUT_STRING, " ");
+        assertThat(spaceCount).isEqualTo(EXPECTED_COUNT);
+    }
+}