Add tests to confirm that the file is not modified if it already formatted (#304)

Summary:
Pull Request resolved: https://github.com/facebookincubator/ktfmt/pull/304

2 tests -
1. File is already formatted, file should not get modified after running the formatter
2. File is not formatted, file should be modified after runnnig the formatter

Reviewed By: cgrushko

Differential Revision: D35295650

fbshipit-source-id: 288bab862e3ee04749da71ba947444ddfa629439

1 files changed, 35 insertions, 0 deletions

diff --git a/core/src/test/java/com/facebook/ktfmt/cli/MainTest.kt b/core/src/test/java/com/facebook/ktfmt/cli/MainTest.kt
index 03660ae..51972ab 100644
--- a/core/src/test/java/com/facebook/ktfmt/cli/MainTest.kt
+++ b/core/src/test/java/com/facebook/ktfmt/cli/MainTest.kt
@@ -21,6 +21,7 @@ import java.io.ByteArrayOutputStream
 import java.io.File
 import java.io.PrintStream
 import java.lang.IllegalStateException
+import java.nio.file.Files
 import java.util.concurrent.ForkJoinPool
 import org.junit.After
 import org.junit.Assert.fail
@@ -162,6 +163,40 @@ class MainTest {
   }
 
   @Test
+  fun `file is not modified if it is already formatted`() {
+    val code = """fun f() = println("hello, world")""" + "\n"
+    val formattedFile = root.resolve("formatted_file.kt")
+    formattedFile.writeText(code)
+    val formattedFilePath = formattedFile.toPath()
+
+    val lastModifiedTimeBeforeRunningFormatter =
+        Files.getLastModifiedTime(formattedFilePath).toMillis()
+    Main(emptyInput, PrintStream(out), PrintStream(err), arrayOf(formattedFile.toString())).run()
+    val lastModifiedTimeAfterRunningFormatter =
+        Files.getLastModifiedTime(formattedFilePath).toMillis()
+
+    assertThat(lastModifiedTimeBeforeRunningFormatter)
+        .isEqualTo(lastModifiedTimeAfterRunningFormatter)
+  }
+
+  @Test
+  fun `file is modified if it is not formatted`() {
+    val code = """fun f() =   println(  "hello, world")""" + "\n"
+    val unformattedFile = root.resolve("unformatted_file.kt")
+    unformattedFile.writeText(code)
+    val unformattedFilePath = unformattedFile.toPath()
+
+    val lastModifiedTimeBeforeRunningFormatter =
+        Files.getLastModifiedTime(unformattedFilePath).toMillis()
+    Main(emptyInput, PrintStream(out), PrintStream(err), arrayOf(unformattedFile.toString())).run()
+    val lastModifiedTimeAfterRunningFormatter =
+        Files.getLastModifiedTime(unformattedFilePath).toMillis()
+
+    assertThat(lastModifiedTimeBeforeRunningFormatter)
+        .isLessThan(lastModifiedTimeAfterRunningFormatter)
+  }
+
+  @Test
   fun `dropbox-style is passed to formatter (file)`() {
     val code =
         """fun f() {