Adds fuzz tests

tests/fuzz_isort.dict

@@ -0,0 +1,4 @@
+"from"
+"import"
+"with"
+"as"

tests/fuzz_isort.py

@@ -0,0 +1,47 @@
+#!/usr/bin/python3
+import sys
+import io
+import atheris
+
+
+with atheris.instrument_imports():
+    import isort
+    from isort.exceptions import ExistingSyntaxErrors
+
+
+def TestOneInput(data):
+    fdp = atheris.FuzzedDataProvider(data)
+    try:
+        isort.api.check_code_string(fdp.ConsumeUnicodeNoSurrogates(
+            fdp.ConsumeIntInRange(1, 1000)))
+        isort.api.check_stream(io.StringIO(fdp.ConsumeUnicodeNoSurrogates(
+            fdp.ConsumeIntInRange(1, 1000))))
+    # exceptions caused by invalid inputs - ignore as uninteresting
+    except (ExistingSyntaxErrors, ValueError):
+        pass
+    try:
+        isort.api.sort_code_string(fdp.ConsumeUnicodeNoSurrogates(
+            fdp.ConsumeIntInRange(1, 1000)))
+        isort.api.sort_stream(io.StringIO(fdp.ConsumeUnicodeNoSurrogates(
+            fdp.ConsumeIntInRange(1, 1000))),
+                          io.StringIO(fdp.ConsumeUnicodeNoSurrogates(
+            fdp.ConsumeIntInRange(1, 1000))))
+    # exceptions caused by invalid inputs - ignore as uninteresting
+    except (ExistingSyntaxErrors, ValueError):
+        pass
+    try:
+        isort.api.place_module(fdp.ConsumeUnicodeNoSurrogates(
+            fdp.ConsumeIntInRange(1, 1000)))
+        isort.api.place_module_with_reason(fdp.ConsumeUnicodeNoSurrogates(
+            fdp.ConsumeIntInRange(1, 1000)))
+    # exceptions caused by invalid inputs - ignore as uninteresting
+    except (ValueError, OSError):
+        pass
+    isort.api.find_imports_in_stream(io.StringIO(fdp.ConsumeUnicodeNoSurrogates(
+        fdp.ConsumeIntInRange(1, 1000))))
+    isort.api.find_imports_in_code(fdp.ConsumeUnicodeNoSurrogates(
+        fdp.ConsumeIntInRange(1, 1000)))
+
+
+atheris.Setup(sys.argv, TestOneInput)
+atheris.Fuzz()