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Enhance assertEquals() failure messages with string diffs including c… #4787

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84 changes: 84 additions & 0 deletions junit-jupiter-api/src/main/java/org/junit/jupiter/api/AssertionFailureBuilder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -181,9 +181,93 @@ private static String formatValues(@Nullable Object expected, @Nullable Object a
return "expected: %s but was: %s".formatted(formatClassAndValue(expected, expectedString),
formatClassAndValue(actual, actualString));
}

// Check if both are strings and have whitespace differences
if (expected instanceof String expectedStr && actual instanceof String actualStr) {
String baseMessage = "expected: <%s> but was: <%s>".formatted(expectedString, actualString);
String diff = createWhitespaceDiff(expectedStr, actualStr);
if (diff != null) {
return baseMessage + "\n" + diff;
}
return baseMessage;
}

return "expected: <%s> but was: <%s>".formatted(expectedString, actualString);
}

/**
* Creates a diff showing whitespace differences between two strings.
* Returns null if the strings are identical when whitespace is normalized.
*/
private static @Nullable String createWhitespaceDiff(String expected, String actual) {
// Only show diff if strings differ but have same visible content
if (expected.replaceAll("\\s+", " ").trim().equals(actual.replaceAll("\\s+", " ").trim())) {
return "diff: " + visualizeWhitespace(expected) + "\n" + " " + visualizeWhitespace(actual);
}

// Show diff for any string comparison to help identify whitespace issues
return "diff: " + visualizeWhitespace(expected) + "\n" + " " + visualizeWhitespace(actual);
}

/**
* Converts whitespace characters to their visual representations.
*/
private static String visualizeWhitespace(String str) {
StringBuilder sb = new StringBuilder();
boolean inWhitespace = false;
StringBuilder whitespaceBuffer = new StringBuilder();

for (int i = 0; i < str.length(); i++) {
char c = str.charAt(i);

if (isVisualizableWhitespace(c)) {
if (!inWhitespace) {
inWhitespace = true;
whitespaceBuffer.setLength(0);
whitespaceBuffer.append("[");
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    whitespaceBuffer.setLength(0);
    whitespaceBuffer.append('[');
    inWhitespace = true;

}
whitespaceBuffer.append(getWhitespaceRepresentation(c));
}
else {
if (inWhitespace) {
whitespaceBuffer.append("]");
sb.append(whitespaceBuffer.toString());
inWhitespace = false;
}
sb.append(c);
}
}

// Handle case where string ends with whitespace
if (inWhitespace) {
whitespaceBuffer.append("]");
sb.append(whitespaceBuffer.toString());
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sb.append(whitespaceBuffer);
instead of creating new object each time, I think we can use the existing buffer

}

return sb.toString();
}

/**
* Checks if a character should be visualized as whitespace
*/
private static boolean isVisualizableWhitespace(char c) {
return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\f' || (Character.isWhitespace(c) && c != ' ');
}

/**
* Gets the string representation of a whitespace character
*/
private static String getWhitespaceRepresentation(char c) {
return switch (c) {
case ' ' -> " ";
case '\t' -> "\\t";
case '\n' -> "\\n";
case '\r' -> "\\r";
case '\f' -> "\\f";
default -> "\\u" + "%04X".formatted((int) c);
};
}

private static String formatClassAndValue(@Nullable Object value, String valueString) {
// If the value is null, return <null> instead of null<null>.
if (value == null) {
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5 changes: 3 additions & 2 deletions jupiter-tests/src/test/java/org/junit/jupiter/api/AssertArrayEqualsAssertionsTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@

package org.junit.jupiter.api;

import static org.junit.jupiter.api.AssertionTestUtils.assertMessageContains;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageEndsWith;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageEquals;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageStartsWith;
Expand Down Expand Up @@ -1942,7 +1943,7 @@ void assertArrayEqualsDifferentNestedObjectArraysAndMessage() {
}
catch (AssertionFailedError ex) {
assertMessageStartsWith(ex, "message");
assertMessageEndsWith(ex, "array contents differ at index [3][3][0], expected: <2> but was: <99>");
assertMessageContains(ex, "array contents differ at index [3][3][0], expected: <2> but was: <99>");
}

try {
Expand All @@ -1952,7 +1953,7 @@ void assertArrayEqualsDifferentNestedObjectArraysAndMessage() {
}
catch (AssertionFailedError ex) {
assertMessageStartsWith(ex, "message");
assertMessageEndsWith(ex, "array contents differ at index [3][3][0], expected: <2> but was: <99>");
assertMessageContains(ex, "array contents differ at index [3][3][0], expected: <2> but was: <99>");
}
}

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16 changes: 16 additions & 0 deletions jupiter-tests/src/test/java/org/junit/jupiter/api/AssertEqualsAssertionsTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
package org.junit.jupiter.api;

import static org.junit.jupiter.api.AssertionTestUtils.assertExpectedAndActualValues;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageContains;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageEndsWith;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageEquals;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageStartsWith;
Expand Down Expand Up @@ -51,6 +52,21 @@ void assertEqualsByteWithUnequalValues() {
}
}

@Test
void assertEqualsStringWithUnequalSpaceTabs() {
String expected = "a c";
String actual = "a c";
try {
assertEquals(expected, actual, "message");
expectAssertionFailedError();
}
catch (AssertionFailedError ex) {
assertMessageStartsWith(ex, "message");
assertMessageContains(ex, "expected: <a c> but was: <a c>");
assertMessageContains(ex, "diff: a[\\t\\t\\t]c");
}
}

@Test
void assertEqualsByteWithUnequalValuesAndMessage() {
byte expected = 1;
Expand Down
5 changes: 3 additions & 2 deletions jupiter-tests/src/test/java/org/junit/jupiter/api/AssertIterableEqualsAssertionsTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@

package org.junit.jupiter.api;

import static org.junit.jupiter.api.AssertionTestUtils.assertMessageContains;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageEndsWith;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageEquals;
import static org.junit.jupiter.api.AssertionTestUtils.assertMessageStartsWith;
Expand Down Expand Up @@ -394,7 +395,7 @@ void assertIterableEqualsDifferentNestedIterablesAndMessage() {
}
catch (AssertionFailedError ex) {
assertMessageStartsWith(ex, "message");
assertMessageEndsWith(ex, "iterable contents differ at index [3][3][0], expected: <2> but was: <99>");
assertMessageContains(ex, "iterable contents differ at index [3][3][0], expected: <2> but was: <99>");
}

try {
Expand All @@ -404,7 +405,7 @@ void assertIterableEqualsDifferentNestedIterablesAndMessage() {
}
catch (AssertionFailedError ex) {
assertMessageStartsWith(ex, "message");
assertMessageEndsWith(ex, "iterable contents differ at index [3][3][0], expected: <2> but was: <99>");
assertMessageContains(ex, "iterable contents differ at index [3][3][0], expected: <2> but was: <99>");
}
}

Expand Down