Use platform-specific line separators

The `System.lineSeparator()` function will return the end of line
separator appropriate for the current runtime, i.e. "\r\n" on Windows
and "\n" on Unix.

Author: albertdev

hamcrest/src/main/java/org/hamcrest/MatcherAssert.java

@@ -10,9 +10,11 @@ public static <T> void assertThat(String reason, T actual, Matcher<? super T> ma
         if (!matcher.matches(actual)) {
             Description description = new StringDescription();
             description.appendText(reason)
-                       .appendText("\nExpected: ")
+                       .appendText(System.lineSeparator())
+                       .appendText("Expected: ")
                        .appendDescriptionOf(matcher)
-                       .appendText("\n     but: ");
+                       .appendText(System.lineSeparator())
+                       .appendText("     but: ");
             matcher.describeMismatch(actual, description);
 
             throw new AssertionError(description.toString());

hamcrest/src/test/java/org/hamcrest/MatcherAssertTest.java

@@ -12,8 +12,9 @@ public final class MatcherAssertTest {
     includesDescriptionOfTestedValueInErrorMessage() {
         String expected = "expected";
         String actual = "actual";
+        String endLine = System.lineSeparator();
 
-        String expectedMessage = "identifier\nExpected: \"expected\"\n     but: was \"actual\"";
+        String expectedMessage = "identifier" + endLine + "Expected: \"expected\"" + endLine + "     but: was \"actual\"";
 
         try {
             assertThat("identifier", actual, equalTo(expected));
@@ -30,8 +31,9 @@ public final class MatcherAssertTest {
     descriptionCanBeElided() {
         String expected = "expected";
         String actual = "actual";
+        String endLine = System.lineSeparator();
 
-        String expectedMessage = "\nExpected: \"expected\"\n     but: was \"actual\"";
+        String expectedMessage = endLine + "Expected: \"expected\"" + endLine + "     but: was \"actual\"";
 
         try {
             assertThat(actual, equalTo(expected));
@@ -78,7 +80,8 @@ public void describeMismatch(Object item, Description mismatchDescription) {
             }
         };
 
-        String expectedMessage = "\nExpected: Something cool\n     but: Not cool";
+        String endLine = System.lineSeparator();
+        String expectedMessage = endLine + "Expected: Something cool" + endLine + "     but: Not cool";
 
         try {
             assertThat("Value", matcherWithCustomMismatchDescription);