Add Gradle output assertions.

^KT-45744 In Progress

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/testbase/outputAssertions.kt

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.testbase
+
+import org.gradle.testkit.runner.BuildResult
+
+/**
+ * Asserts Gradle output contains [expectedSubString] string.
+ */
+fun BuildResult.assertOutputContains(
+    expectedSubString: String
+) {
+    assert(output.contains(expectedSubString)) {
+        "Build output does not contain \"$expectedSubString\""
+    }
+}
+
+/**
+ * Asserts Gradle output does not contain [notExpectedSubString] string.
+ *
+ * @param wrappingCharsCount amount of chars to include before and after [notExpectedSubString] occurrence
+ */
+fun BuildResult.assertOutputDoesNotContain(
+    notExpectedSubString: String,
+    wrappingCharsCount: Int = 100,
+) {
+    assert(!output.contains(notExpectedSubString)) {
+        // In case if notExpectedSubString is multiline string
+        val occurrences = mutableListOf<Pair<Int, Int>>()
+        var startIndex = output.indexOf(notExpectedSubString)
+        var endIndex = startIndex + notExpectedSubString.length
+        do {
+            occurrences.add(startIndex to endIndex)
+            startIndex = output.indexOf(notExpectedSubString, endIndex)
+            endIndex = startIndex + notExpectedSubString.length
+        } while (startIndex != -1)
+
+        val linesContainingSubString = occurrences.map { (startIndex, endIndex) ->
+            output.subSequence(
+                (startIndex - wrappingCharsCount).coerceAtLeast(0),
+                (endIndex + wrappingCharsCount).coerceAtMost(output.length)
+            )
+        }
+
+        """
+        |
+        |===> Build output contains non-expected sub-string:
+        |'$notExpectedSubString'
+        |===> in following places:
+        |${linesContainingSubString.joinToString(separator = "\n|===> Next case:\n")}
+        |===> End of occurrences
+        |
+        """.trimMargin()
+    }
+}
+
+/**
+ * Assert build output contains one or more strings matching [expected] regex.
+ */
+fun BuildResult.assertOutputContains(
+    expected: Regex
+) {
+    assert(output.contains(expected)) {
+        "Build output does not contain any line matching '$expected' regex."
+    }
+}
+
+/**
+ * Asserts build output does not contain any lines matching [regexToCheck] regex.
+ */
+fun BuildResult.assertOutputDoesNotContain(
+    regexToCheck: Regex
+) {
+    assert(!output.contains(regexToCheck)) {
+        val matchedStrings = regexToCheck
+            .findAll(output)
+            .map { it.value }
+            .joinToString(prefix = "  ", separator = "\n  ")
+        "Build output contains following regex '$regexToCheck' matches:\n$matchedStrings"
+    }
+}