Remove OS-specific elements from tests

Author: AbdullinAM

core/src/test/java/com/facebook/ktfmt/cli/MainTest.kt

@@ -349,7 +349,7 @@ class MainTest {
         .run()
 
     assertThat(out.toString(UTF_8)).doesNotContain("hello, world")
-    assertThat(out.toString(testCharset)).isEqualTo("<stdin>\n")
+    assertThat(out.toString(testCharset)).isEqualTo("<stdin>${System.lineSeparator()}")
   }
 
   @Test
@@ -460,7 +460,7 @@ class MainTest {
         .run()
 
     assertThat(out.toString(UTF_8)).doesNotContain("hello, world")
-    assertThat(out.toString(testCharset)).isEqualTo("<stdin>\n")
+    assertThat(out.toString(testCharset)).isEqualTo("<stdin>${System.lineSeparator()}")
     assertThat(exitCode).isEqualTo(1)
   }
 

core/src/test/java/com/facebook/ktfmt/cli/ParsedArgsTest.kt

@@ -287,7 +287,7 @@ class ParsedArgsTest {
         assertFailsWith<FileNotFoundException> {
           ParsedArgs.processArgs(arrayOf("@non-existing-file"))
         }
-    assertThat(e.message).contains("non-existing-file (No such file or directory)")
+    assertThat(e.message).contains("non-existing-file")
   }
 
   @Test